Language / in Polish slang, what is the difference between Siema and Siemka? [64]

A Polish "mate" of mine sent me a text recently with only one word, "Siemka". I've texted back, asking what it means, but no reply yet. It has been bugging me all day. Would someone please tell me what that's all about!

Language / in Polish slang, what is the difference between Siema and Siemka? [64]

Thanks, but it's a bit bizarre, writing only one word in a text, meaning "goodbye", isn't it?? Normally if you wanted to write just one word to someone, it would be a greeting, like "hi", but then maybe this person is just a bit strange. I'm not going to lose sleep over it....!