There are many accounts in the scriptures that decry the seeking of signs.
Consider the example from the life of Jesus Christ:
"The Pharisees also with the Sadducees came, and tempting desired him that he would shew them a sign from heaven. He answered and said unto them, When it is evening, ye say, It will be fair weather: for the sky is red. And in the morning, It will be foul weather to day: for the sky is red and lowring, O ye hypocrites, ye can discern the face of the sky; but can ye not discern the signs of the times? A wicked and adulterous generation seeketh after a sign; and there shall no sign be given unto it..." (Matthew 16:1-4)
The Book of Mormon condemns the seeking of signs in two profound examples:
1. The sign that was given to Sherem was being struck with a debilitating sickness that killed him. (Jacob 7)
2. The sign that was given to Korihor was being struck dumb. (Alma 30)
Contemporarily, teachers in the Mormon faith affirm that seeking signs is negative. I have sat through many classes where instructors have professed that signs are never a good source of testimony. Examples that affirm this position include the following:
1. Pharaoh was determined to pursue after the children of Israel even after blood, frogs, lice, flies, the death of their cattle, boils, hail and fire, locusts, darkness, and the destroying angel. (Exodus 7-14)
2. The children of Israel worshiped a golden calf even after being fed manna from heaven and being miraculously delivered through a split in the Red Sea. (Exodus 14,16,32)
3. Israel tolerated Baal worship even after Elijah called down fire from heaven. (1 Kings 18-21)
4. After the miraculous delivery of Jerusalem from Sennacherib, Hezekiah's son Manasseh turned to wickedness. (2 Kings 19, 21:1-6)
5. Laman and Lemuel doubted the ability of God to help them obtain the brass plates immediately after having an angelic visitation of rebuke. (1 Nephi 3:31)
6. Oliver Cowdrey left the Mormon Church for several years after being ordained to the Priesthood by John the Baptist, as well as a large number of other miraculous witnesses of the divinity of the work.
Certainly, the case that signs are largely futile seems sound. It is not surprising that teachers throughout the church affirm that sign-seeking is negative.
The inconsistency that seems to appear occurs when teachers and missionaries invite people to pray and ask God so that they might personally know whether the Church is led by Jesus Christ, or whether the Book of Mormon is the word of God. If sign seeking is so bad, they why tell people to seek signs?
Another equally important question is that if seeking signs is so bad, why has God ever given them? Why tempt people to seek signs if they should not be doing it?
A concept that seems to be implied by several teachers is the superiority of spiritual evidence over tangible evidence. Some point to the example of Alma, who stated that he knew the truths of the gospel of Christ by the spirit rather than the angelic visitation and vision he encountered in his youth. (Mosiah 27, Alma 38:6) There are also statements by prophets to the same effect. Consider the following from Joseph F. Smith:
“The Spirit of God speaking to the spirit of man has power to impart truth with greater effect and understanding than the truth can be imparted by personal contact even with heavenly beings. Through the Holy Ghost the truth is woven into the very fibre and sinews of the body so that it cannot be forgotten.” (“The Sin against the Holy Ghost,” Instructor, Oct. 1935, p. 431)
Of course, interpreting statements such as these can come across with the implication that a person that has received a spiritual witness will never fall away. This is, of course, incorrect. People that have received spiritual witnesses, even those that have performed missionary service to persuade others to seek spiritual witnesses have in some cases unfortunately fallen from activity and lost faith in Christianity. Recognizing spiritual evidence is not a stamp in the passport that grants passage through the pearly gates.
As unfortunate as these cases are, they highlight the reason that Mormons ask people to pray for spiritual evidence of the Book of Mormon or the prophetic calling of Joseph Smith or the divinity of Jesus Christ. It is one thing to stubbornly refuse to do anything until God proves himself, and it is quite another to diligently and humbly pray for help believing something.
Consider the man who begged Christ for help with his child:
"And one of the multitude answered and said, Master, I have brought unto thee my son, which hath a dumb spirit; And wheresoever he taketh him, he teareth him: and he foameth, and gnasheth with his teeth, and pineth away: and I spake to thy disciples that they should cast him out; and they could not. He answereth him, and saith, O faithless generation, how long shall I be with you? how long shall I suffer you? bring him unto me. And they brought him unto him: and when he saw him, straightway the spirit tare him; and he fell on the ground, and wallowed foaming. And he asked his father, How long is it ago since this came unto him? And he said, Of a child. And ofttimes it hath cast him into the fire, and into the waters, to destroy him: but if thou canst do any thing, have compassion on us, and help us. Jesus said unto him, If thou canst believe, all things are possible to him that believeth. And straightway the father of the child cried out, and said with tears, Lord, I believe; help thou mine unbelief. When Jesus saw that the people came running together, he rebuked the foul spirit, saying unto him, Thou dumb and deaf spirit, I charge thee, come out of him, and enter no more into him. And the spirit cried, and rent him sore, and came out of him..." (Mark 9:17-26, emphasis added)
This story is an excellent example of being humble and diligent. The man had already gone to the disciples, and they were unsuccessful. He appealed to the Son of God himself, and asked not only for help with his son, but help to believe. The miraculous outcome was not a method of proving that Jesus was the Messiah, but a method of providing mercy and compassion to a child of God that persisted in seeking his power.
The invitation that is made by Moroni and repeated by missionaries across the world is not to do nothing until God proves himself with a sign. It is to actively seek him:
"Behold, I would exhort you that when ye shall read these things, if it be wisdom in God that ye should read them, that ye would remember how merciful the Lord hath been unto the children of men, from the creation of Adam even down until the time that ye shall receive these things, and ponder it in your hearts. And when ye shall receive these things, I would exhort you that ye would ask God, the Eternal Father, in the name of Christ, if these things are not true; and if ye shall ask with a sincere heart, with real intent, having faith in Christ, he will manifest the truth of it unto you, by the power of the Holy Ghost. And by the power of the Holy Ghost ye may know the truth of all things." (Moroni 10:3-5, emphasis added)
Understanding of the truth is unlikely to come with a casual curiosity or when demanding proof before action. Christ did not say "wonder, and ye shall receive, demand and ye shall find, wait for a knock before you open." He did say:
"Ask, and it shall be given you; seek, and ye shall find; knock, and it shall be opened unto you: For every one that asketh receiveth; and he that seeketh findeth; and to him that knocketh it shall be opened." (Matthew 7:7-8)
The form of sign seeking is different from the type that is condemned. A better term to describe this type of sign-seeking is faith. "But without faith it is impossible to please him: for he that cometh to God must believe that he is, and that he is a rewarder of them that diligently seek him." (Hebrews 11:6) It is the difference between Alma and Korihor, and the variance between Nephi and his brothers Laman and Lemuel. In the end, it is faith that keeps people doing the right thing, and that brings understanding, wisdom, and knowledge. Ultimately, it is unbelief that causes people to neglect what is right, and that leads them to fall away.
One witness is not better than another witness. There is nothing wrong with a person believing that God is real after seeing a miracle. There is nothing superior about spiritual feelings that can accompany the learning of true principles.
That having been said, diligently and consistently believing in God is superior to demanding justification for every commandment. The invitation to come to Christ is superior to the idea of waiting until he comes to you. Asking to prove oneself to God is superior to asking God to prove himself... and in all cases, faith is superior to doubt.