If someone snaps their fingers at something or someone, it is a way of saying they don't think very much of it or them. If you snap at someone, you speak an act in an irritated way towards them. "She snapped at him when he kept asking about her personal life." "I was just asking when supper was. You didn't have to snap at me." If you snap for someone, it means that you snap your fingers as a signal that they should come and do something for you. It was a way of summoning servants. It is considered insulting to use it now for many people. It I want to get the attention of a waiter, for example, I would wave my hand, not snap my fingers.

It means 'He ignores and disregards of the speed limit." We should use the prep. 'at'