Is a chop or Jitsu-in type=signed for the purposes of authen?

[larkvi]

there is an existing stamp element that can be turned into an authenticating element, like seal, but should stamps used as signatures be treated as scuh (like notarial marks or crosses) or should they be their own category?

Also: Should adhesive stamps with kinegrams, like those on computers, establishing authentic make, be treated as another category?