Anon, if you don’t feel comfortable, there is no reason for you to tell people that you’re kin. Its not something anyone *needs* to know about you. Unlike your gender or your sexual orientation its not something that effects anyone around you, or the way that you should be treated in public. Its a private belief that you can share, or keep to yourself as much as you want.
If anyone you mention “needs” to know, its maybe your girlfriend, if the two of your are really serious, and that’s only because I believe that people who are sharing a life together should be able to discuss beliefs and anything else together and accept one another.