Is a ring marked with ci 10k real?

If you're asking if it's really 10 karat gold ... do you think that someone who would make a ring of brass (or whatever) and try to pass it off as gold would be morally above counterfeiting a marking, or do you just think that would be too hard so they wouldn't bother?

If you want to know for sure if your ring is "real" or not, take it to a jeweler for testing. Markings mean approximately nothing.