Well, had $3.

If there will be an indicator like that, people may assume that the account that doesn't have it is worse in some way.

A signal that you're willing to pay something. The amount here isn't really relevant, and usage goes beyond social signaling.

If it's exposed over the API and someone's logging into my product with that flag set, you could reasonably assume it's not a bot, or at the very least that whoever's botting has paid $3 of their own money.

Had. Last month.