Is it a sin to ask God for a sign?
Gideon did it twice and God answered both times

In short
The Bible contains people who ask for signs and receive them, and people who ask for signs and are rebuked. The difference is not the request but the posture: Gideon asked while obeying, and the crowd asked instead of believing. That distinction is the whole answer.
What the text says
And Gideon said unto God, If thou wilt save Israel by mine hand, as thou hast said, Behold, I will put a fleece of wool in the floor; and if the dew be on the fleece only, and it be dry upon all the earth beside, then shall I know that thou wilt save Israel by mine hand, as thou hast said. And it was so: for he rose up early on the morrow, and thrust the fleece together, and wringed the dew out of the fleece, a bowl full of water. And Gideon said unto God, Let not thine anger be hot against me, and I will speak but this once: let me prove, I pray thee, but this once with the fleece; let it now be dry only upon the fleece, and upon all the ground let there be dew. And God did so that night: for it was dry upon the fleece only, and there was dew on all the ground.
Isaiah 7:11 was the verse of the day on June 27, 2022. See that day
Often brought inIsaiah 7:11
Ask thee a sign of the LORD thy God; ask it either in the depth, or in the height above.
Ahaz is told to ask for a sign and refuses, dressing his refusal as piety. He is the one criticised, which turns the usual assumption around.
The counterweightMatthew 12:39
But he answered and said unto them, An evil and adulterous generation seeketh after a sign; and there shall no sign be given to it, but the sign of the prophet Jonas:
Jesus refuses a sign to people who have already seen many. The rebuke lands on those using the request to postpone a decision they have made.
What Christians agree on
God is not obliged to answer, and a sign is not a substitute for what he has already said. Nobody teaches that asking is forbidden, and nobody teaches that it is owed.
Where they disagree
Those who read Gideon as permission
God met a frightened man where he was. He still does, and asking for help to believe is not the same as demanding proof.
Those who read the gospels as caution
Jesus calls sign-seeking the mark of a generation that will not commit. Where the will is already clear, asking for a sign is a way of not deciding.
Those who focus on guidance
Signs are a poor method for decisions. Scripture, counsel and honest reasoning are the ordinary means, and a fleece often just outsources a choice you should make.
Questions worth asking
- Do I want help to obey, or a reason to delay?
- If the sign came and pointed the way I do not want, would I follow it?
- Is there something already clear that I am hoping a sign will overrule?
Gideon asked twice, out of fear, after he had already been told what to do - and God answered. There is more room here than the anxious version of the question assumes.

