Sometimes they put a sticker on the outside: "Off-Road Use only"
Otherwise, as Jim said, carefully open the case, and gently separate the two big printed circuit board. You'll either see a socketed daughterboard, with the main ecu in a square socket, and two EEPROMS in two rectangular sockets, or you will see the main ecu still soldered to the motherboard.
Some have a sticker. Some have humps. There are a couple different internal configurations so some don't require humps at all. All the ATS Rom Tunes have a 1/4 inch spacer that makes the ECU slightly thicker. Doing that means we don't have to relocated components on the board to make room insiude the tight ECU. It increases reliability because we are't adding traces or extending wires to components that should be surface mounted.