Didn't know that there will be discussion on watermarking…
There are few reasons I'm doing it.
Often - when I look for some stuff in the net - I want to see more pictures, compare my card etc. it is easier to find it and seek for owner or his collection to get more info or more photos… the same thing is done for example by easy_john, amoretro, enigma, yjfy.com, even Artex photos even if there is no watermark are allways on the same light brown background so when I see one in google graphics I know this is his photo etc - i think it's helpful and OK... it helped me many times to find some more pictures, data etc. that way.
Maybe by this watermark someone will visit my website and see my collection - why not. Maybe find some mistake, or write to me to ask about something or be willing to trade... why not?
For me it has nothing to do with my "artistic photography" hahah copyright or to prevent stealing and useing it by someone... oh come on! Yeah but it's easy to call it childish, ridiculous, pointless… blah blah blach