Tues Gitten 9

The gemara says that we allow illiterate witnesses to sign. Although they can't sign their names , but we cut the parchment with their names, and they will trace it.

Rashi explains "cutting" that we scratch the parchment. Although their names are already etched there, it wouldn't be a problem of writing over writ (which we don't consider it as a writing) since etching is not in ink, so it's much weaker than the covering ink, so the writing in ink is considered as its own writing.

Tosfos doesn't believe that etching is a good definition of "cutting." Therefore, he explains that it means that they cut out stencils of their names. We must say that they cut out thick letters, so the witnesses can trace it in their own style, so that we can verify the signatures later, and it wouldn't be just a generic tracing of a stencil.