The account of Jacob's encounter with Sherem in Jacob 7 is multilayered and interesting on many levels. I just noticed one additional layer, involving what happens right after Sherem dies:
21 And when the multitude had witnessed that he spake these things as he was about to give up the ghost, they were astonished exceedingly; insomuch that the power of God came down upon them, and they were overcome that they fell to the earth.
Notice how this verse mirrors what had recently happened to Sherem a few verses earlier.
15 And it came to pass that when I, Jacob, had spoken these words, the power of the Lord came upon him, insomuch that he fell to the earth. And it came to pass that he was nourished for the space of many days.
Sherem had demanded that Jacob show him a sign:
13 And it came to pass that he said unto me: Show me a sign by this power of the Holy Ghost, in the which ye know so much.
Instead, what happened to him became a sign for the people.
22 Now, this thing was pleasing unto me, Jacob, for I had requested it of my Father who was in heaven; for he had heard my cry and answered my prayer.
23 And it came to pass that peace and the love of God was restored again among the people; and they searched the scriptures, and hearkened no more to the words of this wicked man.
Jacob's prayer is found in verse 14:
14 And I said unto him: What am I that I should tempt God to show unto thee a sign in the thing which thou knowest to be true? Yet thou wilt deny it, because thou art of the devil. Nevertheless, not my will be done; but if God shall smite thee, let that be a sign unto thee that he has power, both in heaven and in earth; and also, that Christ shall come. And thy will, O Lord, be done, and not mine.
The fulfillment of Jacob's words certainly did provide a sign for Sherem, as he requested, though not to his benefit. What befell him brought about an awareness in him of his awful state before God. The people who witnessed this were also wrought upon by the power of God, causing them to "search the scriptures" and restoring "peace and the love of God" among them, "[hearkening] no more to the words of this wicked man."
What I take from this is that we will all receive the witness we desire, at some point or another. If we seek it willingly and humble ourselves, the signs provided to us by the Holy Ghost and holy works will allow us to stand clean before God at the day of judgment.
The proper order is for faith to precede the signs. Satan tries to trick us into believing it goes the other way around -- seeing a sign first, only then being willing to believe.