Which finger do I wear my promise ring on?

I'm leaving for the navy and my girlfriend bought me a ring and the ring is a promise that I will be back. I bought her a ring as well but I'm not sure which finger to wear it on the kay's lady told me to put it on my right Hand but my friend said that I'm supposed to put it on my married finger but I was like dude were not getting married it's just a promise ring and he was like I know, the ring isn't a wedding band but your supposed to wear it on the married finger cuz if it's on the other hand it means your divorced. Idk????