The way you know who repped you:
-- They sign their rep. (And some sign with just initials.)
You can guess in other ways:
-- If only one person liked your post, and you got a rep, chances are good it's the person who liked your post.
-- Once you get to know people better on here, you can sometimes tell from what they say with the rep. (For, example, I tend to "lol" often, and say things like "yup" when I write and when I rep people.)
On the other hand, if someone doesn't tell, then it's that thingy Jesus told us to do, keep our deeds quiet, so we're not boasting. I often give no hints I'm the repper, because it's not about me. It's about you. (And, nope. Don't think I've repped you yet. And, if I do, I'd be all kinds of flustered if you thank me for it. Just something to think about, although there are people who do like being thanked.)