If you seal the flap of a letter to prevent tampering, can't someone just swap the envelope and possibly forge your signature?
Slickterp
Sure.
The Mikel
Simple, Sure.
Morningfox
Of course "someone" could do that. They could get hold of _any_ example of your signature and try to forge it. They might dig up you old school paper from 20 years ago. But (1) it is very very difficult to forge a signature, and it is not very hard to detect. More importantly, (2) it is is very very rare, I would guess only a few thousand cases a year, out of a population of many hundreds of millions. And almost all of those cases fail.