Sorcerous Runes

This mystical tattoo looks like pages of text inked upon your body.  Each time you reach an odd level in the sorcerer class (1,3,5,7.etc..) you unearth part of the meaning of the tattoo, which holds the power of the arcane.  You learn one additional sorcerer spell, which must be of a level for which you have spell slots.  These spells don't count against your maximum spells known.