I've mostly noticed two forms of this:

Floors labeled as Club, Executive, Gold, etc., usually by the elevators.

Specialty suites with signs like Presidential Suite, Royal Suite, Regent Suite, etc., on the door and sometimes near elevators and corridor intersections with directional arrows.

I wish every hotel would post the room category inside the door so that I can verify whether I was given the room category I booked or some upgrade the front desk agent said. However, it's better if there's nothing outside of the room to suggest occupancy, such as "deluxe single."