I have spotting on the top of my head too. I've been burnt to a crisp a few times since going sly and burnt many times when I had a buzzcut that had pratically no sunlight-blocking abilities whatsoever. When I had a buzzcut I never wore a hat or put sunscreen into my hair, so my scalp has been abused a lot.
These spots seemed to fade a little bit once I became more protective of my skin, but they are still very much there. They worry me because if they really are the result of sun damage then do I have a ticking time-bomb on my head? Will they eventually sprout little melanoma growths? I don't know. My dermatologist doesn't seem concerned either.