Stickers were introduced in Counter-Strike: Global Offensive with the February 5, 2014 update and are purely cosmetic addition to customize a player's weapon.
A sticker from the player's inventory can be applied only once to any gun or gun skin owned, after which it will be removed from the player's inventory and only exist on the weapon it was placed onto. Trading the weapon skin will carry the applied stickers with them, though stickers applied to vanilla skins (stock weapon skins) cannot be traded since vanilla weapon skins cannot be traded.
