A fellow I worked with whose loose prints (not dry mounted) were collected signed in verso (on the back) in pencil, and on the front on the white border lower right, in pencil also, such that the signature would be covered when over matted, as at an exhibit. So that the pencil would stick, he removed a small rectangle of the emulsion.
For this ritual, which he thoroughly enjoyed, he had a small piece of mat board with the rectangular signature window cut out. He placed this on the print, and with and architect's electric eraser took off that area of the emulsion, then signed. Just one style, that was his.