@Tikibo I don't think they're any more secure than a regular signature with a pen would be, I mean there are shops selling these stamps in bulk over in Japan (for common family names). They're called hanko (or inkan) stamps and traditionally these stamps are used to sign official documents.

As for the security, the point of signatures in the eyes of the law is generally just to have a written acknowledgement of agreement, the sguiggle you actually write down doesn't matter, be it just a simple X, your name or a drawing of Cthulhu. For any kind of verifiable security you'd have to go beyond simple signatures or stamps. I guess that's the point of having impartial witnesses.

I have no idea how those seals work. How hard would it be to falsify them?

Imagine having so much fun at work that you forget you get paid for it. That's the life right there.