guild bound bank items?

Just a passing musing: what if some items in a guild bank could be marked as guild bound? When guild members remove them from the guild bank they can use them, or trade them to fellow guildies, but be blocked from passing them to non-guild members (including via mail and the auction house). If a guild bound item is removed, and the member then /gquits (or transfers off-server), the item should be removed from their inventory and mailed to the GL.

One way to put a stop to bank ninjas?