I’m gonna guess the shirt is meant as an unironic “Checkmate atheists.” Insular social groups tend to forget that the things that they care/feel strongly about might not even be on the collective radar of everyone else - print those things on a shirt and sometimes objective hilarity ensues because it opens the wearer up to outside interpretations that run counter to their intended meaning.

On the other hand, they could be a witchy lesbian, or be showing unironic support for their favorite witchy lesbian in their life. That would be cool, but I’m not betting on it.