Yeah - the overhead tracks are pretty obvious, and the entrance will be on the side of the street on which you've just gotten off the bus (the North side).

The signage on street level isn't very good, and it certainly won't be bustling.

The thing about the station at 125th is that it's heavily used by people commuting between uptown Manhattan and Westchester/Connecticut. At a certain point at night, my experience is that people start going to Grand Central because it feels safer. That makes 125th Street Station get pretty quiet. You'll be getting there around that time.

Just don't get lost. Stay on 125th Street, and it should be cool.