Upon signing up I couldn't use my preferred three-characters username


If I typed one character it would show up as red, but two or more were black. Despite this I was unable to sign up with my preferred username which is three characters long in either Firefox or Chrome. No error was displayed either. If I tried to pick a username that was already taken, I would see an error.

Assuming it isn’t possible to use such short usernames - is it possible to get a seemingly abandoned username (it’s been inactive for over two years)? I could upgrade to premium if necessary.