Guild Signet

From Guildmasters' Guide to Ravnica, page 178.

Description
Ring, uncommon (requires attunement)

This ring, adorned with the symbol of a guild, allows you to cast one spell closely associated with that guild, as shown in the Guild Signet Spells table. A guild signet is sometimes awarded to a guild member whose renown score in that guild is 5 or higher, as a reward for performing special services for the guild. Aside from its magical properties, the ring is also an indicator of the guild's recognition and favor.

A signet has 3 charges, and it regains 1d3 expended charges daily at dawn. While wearing it, you can expend 1 charge to cast the associated spell (save DC 13).