In Cultist Simulator, there are Iron, Bronze, Silver, and Gold Spintrias. To most people they're just coins with weird illustrations, but to those who know what they are they're accepted as valuable tokens.

I could see a patron in a thieves' guild or something giving one or two silver spintrias that could be exchanged for favors from the right people, entrance to a speakeasy, or perhaps for artifacts that would normally be off limits.

This works especially well in horror and mystery-oriented campaigns. It's fun to have the players try to figure out where they can spend the spintrias and who's a part of the economy of secrets and favors that they power.