What happens if one forgets to sign his or her signature on the first?
Doesn't matter. Even if you sign and then struck it off then also your paper would be checked. However your invigilator might be asked if you were present or not. But never commit such mistakes. In the worst scenario they will send for verification in the school of yours. But that rarely happens. Coz they know students sometimes forget these things may be because of pressure of the paper.