As someone who makes his living as a painter, the only paintings I don't sign are the ones I'm not happy with. I will generally destroy a painting I'm not happy with, although my standards are higher now than when I started out. If I am truly proud of my creation, you can be sure I will sign it. It's human nature. If someone goes to the effort of making a truly high quality gun, I see no reason why it would be unattributed, unless it was a guild policy not to do so, or the maker wasn't as enamored of it as we might be.

Similarly, I would doubt the paintings Rembrandt left unsigned were ones he thought that highly of either. Given that, a napkin with his signature on it would sell for outrageous $ now, simply because of his name.

Imagination is everything. - Einstein