Think like this: when people "steal" other people's work they're being assholes for not giving credit, but in the end they're just helping spread the work. On the other hand, when artists go out of their way to make sure people know *they* did something by adding invasive signatures and the like, they are decreasing the quality of their work and sometimes even ruining it completely. That's a lot more harmful than the former.
Sadly, a lot of people are in this not for the art or some good cause, but for attention whoring.
You know what is sad about such statements? The ones that should read it won't do it. And even if they would do, they will not give a shit about it. You know how many times I have found my works on Icanhazcheeseburger or other 'funny' webpages?
a reminder of license seems to be useful Though, you should do the difference between downloading and using without askink or crediting, as downloading has no need for asking you for permission, as long as it is technically allowed by you. It would be clearer Leo, I think. Anyway, respecting license seems to be something some wants to ignore here, and I understand your concern my friend...