Does a blue star tattoo behind the right ear mean a person is a lesbian?

It can be, because lots of pride flags have blue stars, though a more telling symbol of homosexuality would be a rainbow necklace or bracelet.

Historically speaking, Lesbians from the '40s and '50s would tattoo blue stars on their wrists. These tattoos could be covered by watchbands during the day and displayed at night (at clubs and such). Many lesbians choose to honor the history with blue stars of their own. However, the mark does not necessarily mean lesbian, and the location is also varied.