Watch List notes:

UNCERTAIN. Unknown, 1st Century AD. (Bronze, 20 mm, 4.55 g), original coin completely defaced. square countermark with AMOR "Amorium" . cf. Howgego 604 . A well struck countermark. Only one known example to Howgego. Similar examples in auctions from Topirusare under Caracalla all have a circular countermark. Very fine.
From an American collection.

This monogram appears to represent the letters AMOR for Amorium.