Skittles does the exact same thing with his beak. He will rapidly rub the side of his beak against my finger nails.
Aggressive attention getting is hard to miss. It's certainly not something you want to encourage, but if it's play-nibbling - that's different. Skittles likes to play nibble, he likes to 'do battle' with my fingers. It doesn't hurt when he does that. When he gets nasty because I try to take something from him or remove him from a certain area, I don't tolerate that. I say 'no biting'. He knows the difference as do I.
The key is not letting it get out of hand. To not let play biting become aggressive biting.