Siege Modification is a uncommon Enchantment — Aura card from Aether Revolt (AER), collector number 99. Current market price: $0.26 (foil $0.40), TCGplayer market prices via Scryfall.
Enchant creature or Vehicle As long as enchanted permanent is a Vehicle, it's a creature in addition to its other types. Enchanted creature gets +3/+0 and has first strike.