Initiation medal

From Memory Alpha, the free Star Trek reference

An initiation medal was a small, coin-shaped object passed down between members of a Xindi family.

Crewman Daniels gave Captain Jonathan Archer the initiation medal of a crewmember serving aboard the USS Enterprise-J in the 2550s to help him prove to the Xindi Council that he had been to the future. Though quantum dating proved the medal was from the future, the Council was not convinced of Archer's tale. (ENT: "Azati Prime")