Sigiled Sentinel is a common Creature — Human Knight card from March of the Machine (MOM), collector number 37. Current market price: $0.08 (foil $0.13), TCGplayer market prices via Scryfall.
Backup 1 (When this creature enters, put a +1/+1 counter on target creature. If that's another creature, it gains the following ability until end of turn.) Vigilance