Who has claimed that signs lead prophecy? Again, nobody. You're tilting at wind.
Those who desire a sign it must lead to believe and confirm something or men who turn the law upside down as something to seek after would not seek after it hoping it will confirm something. Most say it confirms a person has the Holy Spirit or is filled with the Holy Spirit . What do you think the sign of tongues or any sign in the bible that follows confirms ?
I say the other way around the signs confirm men do not believe prophecy, the word of God, in any language .Prophecy leads a person to believe God. (no outward sign)
In the law it is written, With men of other tongues and other lips will I speak unto this people; and yet for all that will they not hear me, saith the Lord.Wherefore "tongues" are for a sign, not to them that believe, but to them that believe not: but prophesying serveth not for them that believe not, but for them which believe.1 Corinthiasn 14:21 -22