Upload & Sell: Off
Well, that just shows that there is differing experience! I've only been doing it for four decades, but my observation and experience is different. In my experience, the signature goes on the mat because signing the artwork itself has not been considered archival by the Library of Congress (unless done lightly in pencil).
As for it being so emphatically "WRONG!" I'll only quote GB Shaw, "Forgive him. He is a bararbian. He thinks the customs and traditions of his tribe are the laws of nature."
I guess you've been doing it WRONG for 40 years. I guess that's the difference between you and Rhyder. I'll just use the same quote for your efforts "Forgive him. He is a bararbian. He thinks the customs and traditions of his tribe are the laws of nature."
I've been dealing with artists of all kinds on both coasts for many years and I've yet to see one that signed a mat. But I HAVE seen it done at "Art Fairs" where the amateurs have their tents. I have quite a collection of signed prints, not one of them were signed anywhere but the print. Some sign on the back, some on the front, but never on the mat. If I were to come across a print signed on the mat I would immediately suspect a fraud. If you made your assertions at a museum or a reputable gallery, they would "be kind to you and give you a little salt". It an very old european quote that means someone's elevator isn't stopping on all the floors.
BTW. Lithographs and etchings are "signed lightly in pencil" many photos are signed with an acid free ink.