@giana -- the AI is not "forging" anything. But it has been trained with works that do contain signatures, watermarks and the like. So it will sometimes produce artifacts that may, if you squint hard enough, resemble something like writing. Because it has learned "if art then signature"; in other words it thinks those artifacts are supposed to be in the image. It is neither forging nor concealing anybody's actual mark, but it does at times invent something along that line. This is more likely to happen if you have a name in your prompt, especially as an artist's style. How do I know? Well, I once prompted "watercolour paintings in the style of This Fictional Artist I Just Invented" to test that out. Lo and behold! Stable Diffusion kept trying to put what it thought was my make-believe artist's name on almost every one. Take the name out of the prompt, the artifacts disappear. Because they were made up, not copied from any actual artist's work.

Hallucinating. I think that's what they call it when an AI makes stuff up just because. Weird. Undesirable. But certainly not a crime.