My personal lolcow (who is a much worse, and even more delusional about her abilities, artist than Polissa, does the same thing. Massive watermarks that prevent not only unauthorized use of the art, but hinder the viewer's ability to see it, are a hallmark of untalented artists who grossly overestimate the rest of the world's desire to steal their work.
(That said, while Polissa's drawing skills are rudimentary at best and she has no eye for composition, she at least keeps her colors bright and clean, and tries to make tidy, visually appealing work. Most lolcow artists act like they're a year old and smearing their own feces on the wall above their crib again, and their art looks like it. That, or they make shitty drawings colored with markers that look like they were drawn during a particularly boring Algebra class by a 14-year-old. Polissa's work is by no means good, but she's practically a savant when compared to other cows.)