Tattoo

It is suspected that the Roman campers get tattoos that have their parent's symbol (Jason has an eagle for Jupiter) and possibly how many years they've been at the camp, similar to the camp beads at Camp Half-Blood. The tattoos also have markings on them that are similar to a bar code. Jason Grace, who comes from the Roman camp, has a tattoo labeled SPQR with an eagle on it, indicating his father (Zeus/Jupiter).