Signs are rarely given to the wicked to convert them. However, the signs at the birth and death of Christ were given for the explicit intent that there should be no cause for unbelief among the children of men (v. 28). The wicked, however, used this prophecy as a ruse to persecute the believers. They had planned the wholesale, mass murder of the righteous if Samuel's prophecy did not come true, Now it came to pass that there was a day set apart by the unbelievers, that all those who believed in those traditions should be put to death except the sign should come to pass, which had been given by Samuel the prophet (3 Nephi 1:9).
The very next day, the sign was given, and the people were astonished and frustrated. Most of them converted in spite of Satan's efforts to explain away the signs. However, a testimony built on signs alone is the weakest of all testimonies. The wonder and amazement of a sign fades as quickly as mortal memory. Accordingly, within a span of several years, the Nephites were back to their wicked ways (see 3 Nephi 1-2).