Exactly five of my "normal life" friends know that I'm kinky, and four of them are kinky as well (the fifth is my best friend, who I don't really keep secrets from).
It is necessary for me to keep kind of quiet about it, since I'm working toward becoming a professor and your reputation can make or break you on the job market. (Also, just imagine having your students find out? I would not be teaching Human Sexuality, by the way.) And my parents would just be horrified and wonder what went wrong with me...
Occasionally I get so sick of how vanilla and boring the town I live in is, though, and wind up wearing jewelry or accessories that could subtly flag to people in the know that I'm dominant. But so many people in the regular world have borrowed aesthetics from SM that I think it is safe to wear my pieces quietly.