The barbed bow is a vanity item offered as an occasional in-game benefit from RuneScape Game Cards. It has the same stats as a standard Shortbow and can only fire up to iron arrows. When Redeeming either a 90 or 100 days Game card, you also receive 200 iron arrows free to use with the bow. It was given out from the 9th of March to the 31st of March 2012 or by purchasing the gold membership package between 20 December 2012 and 31 January 2013.
It was also made available via:
United States: Gamestop, United Kingdom: GameStation, GAME & GAME Wallet, Canada: EB Games (newly available), Australia & New Zealand: EB Games, Republic of Ireland & mainland Europe: Gamestop
The bow can be kept on death if it's one of your protected items, but otherwise does not appear under your gravestone and will be lost, but it can be retrieved from Diango.