In the Halloween episode with Ethan and Eyghon, Ethan tattoos Buffy with the symbol to deflect the demon off himself. He then burns off his tattoo, etc. Later, in school, Buffy says that she has to spend all her allowance on removing the tattoo without her mom noticing. She then turns around. For starters, she's wearing a spaghetti strap top, dense!! Second and more important, the mark of Eyghon was very clear on her shoulder when Ethan marked it on, but now it's gone! I thought her hair must have been covering it, but she tosses it around so much that you really can tell there is no tattoo!