This page contains information regarding Star Trek: Discovery, and thus may contain spoilers.
The Proficient Service Medallion was a medal awarded for proficient service by an officer in an service organization. Such a medallion was known to be issued by both Starfleet and the Cardassian military.
Sometime during his Starfleet service in the mid-23rd century, Christopher Pike was awarded this medal. It, along with other awards, was listed in the commendations section of Pike's personnel file. (DIS: "Brother")