Signature can be written as a copy of a work, and these words can also be written on the back. Or don't sign it at all

On the issue of copyright, the law clearly stipulates that copyright protection cannot be lifted until 50 years after the birth of a work, so if you copy an ancient painting or an old work, there is no problem, but if it is a recent work, you need to get your own or your family's consent, otherwise you may get into a lawsuit. There have been many such lawsuits in recent years.

Copying works can be sold, and a large part of the paintings sold in the market are copying works. Of course, when you sell it, you must mark it as an imitation, and the price is obviously different from the genuine one.