Your search for "Simic Signet 252" revealed the following:
Simic Signet (DSC) from Duskmourn: House of Horror Commander, available at 401 Games Canada. Rarity: Uncommon Finish: Normal Artist: Mike Sass Card Text:1, T: Add GU
Simic Signet - Dan Frazier is Back: Enemy Signets (SLD) from Secret Lair Drop, available at 401 Games Canada. Rarity: Rare Finish: Normal Artist: Dan Frazier Card Text: Dan Frazier: Enemy Signets1, T: Add GU to your mana pool.