Threefold Signal is a mythic Artifact card from New Capenna Commander (NCC), collector number 111. Current market price: $0.56 (foil $0.40), TCGplayer market prices via Scryfall.
When this artifact enters, scry 3. Each spell you cast that's exactly three colors has replicate {3}. (When you cast it, copy it for each time you paid its replicate cost. You may choose new targets for the copies. A copy of a permanent spell becomes a token.)