Ummm... I'm not sure where on earth we're getting the idea that spray paint is not heavy enough to affect the head. Spray paint is pretty solid, especially if you get a bunch of it on there. A better bet is to use colored sharpies or pencils (not too sharp).
A good number of years ago, I picked up a used Ludwig set that used to belong to a high school. It still had the high school's mascot painted on the reso head. Well, I was poor at the time and couldn't afford a new head, but didn't want the bloody mascot on the front of my drums, so I gave the head to my mother (she's an artist), who painted the whole thing black with a nifty personalized logo for me. It didn't resonate for crap (oil based paints are extremely heavy), but it certainly looked cool. I now have that head displayed in my music room.