Siege Veteran is a rare Creature — Human Soldier card from The Brothers' War Promos (PBRO), collector number 25p. Current market price: $0.49 (foil $2.91), TCGplayer market prices via Scryfall.
At the beginning of combat on your turn, put a +1/+1 counter on target creature you control. Whenever another nontoken Soldier you control dies, create a 1/1 colorless Soldier artifact creature token.