There are two different types of siren graphics, the ones who drop combs actually have combs in their hair in the graphic. The ones who drop the Lock of Siren Hair are wearing skirts made of leg bones. They dont randomly spawn at the same spot, if you have a comb dropping siren in a spot, the one that spawns there will always be a comb dropping type (though it could be any one of the three that drop them).
Ok killing these sirens is a SERIOUS pain in the *** because they will resist spells a lot, but here is a few hints: With my necro i would pull with dispell magic, and then try to land my snare dot. This would USUALLY work, but there were a few sirens who i pulled this way, still got reflects on, and got unsnared when i dispelled them. The "Lock of Siren Hair" (not "Siren Hair") drops from mobs which con darkblue at level 75, the combs from mobs which con lightblue. There are a lot of lightblue sirens in the souteast part of the island. The easiest way for a kiter is to just kite them along the beach, through the water or over the ridge near the beach. there are a few skellies on parts of that ridge though.
Good luck all. I died a LOT on those sirens, i'm glad i dont have to see them again any time soon since i'm done there.