Oh yes, watermark all your smileys. Problem solved.

If you don't want your car stolen, don't buy a car! Put that brain into first gear!
Come on, it's nobody's right to take other's work without permission. It doesn't matter if it's large or small, the fact is something put time and possibly money into making it. It's irresponsible and self-centered to claim that you should be allowed to steal something because the person who created the work "didn't stop you" properly with a watermark or by not publishing them at all. Anything else is just an attempt to justify your own theft.
I ask every single time and if I don't get permission, I don't use. I've even gotten free use of copyrighted paid-for images because I had sufficient respect to ask, perhaps because they were so surprised to find someone who doesn't believe theft is a right via the internet.