It's the acetone in hairspray that'll dissolve the ink, but you wouldn't want the sticky hairspray to remain. If you've got any acetone (nail varnish remover) that'll work better by itself.
Any mild solvent, isopropyl alcohol, meths, etc will work, just use sparingly and might want to use some leather moisturiser cream or something afterwards as solvents will dry the leather out as well as remove the ink.