Cisco Unified Communications Manager Express (CME) and the UC500 appliance ran call control inside a Cisco router. They’re a separate code base from the big CallManager / CUCM.
What you hear
Music on hold on CME points at an audio file in the router’s flash memory, set with a moh <filename> command. We found no evidence that CME shipped a bundled track the way CUCM ships Opus No. 1. So what you hear is whatever an installer loaded, or nothing at all if nobody did.
How to tell it apart
Cisco phones on the desk + hold music that isn’t Opus No. 1 = very possibly CME. Confidence is low here. If you have a CME box with a factory file on it, tell us.