The top is where you see the little chain looking stitches. If you only see 1 thread going sideways at the top of the piece, then it is upside down. There is a difference in how each stitch looks too. I wish I was at home, I could take a picture and post it, but I won't be back for several days.
Although this page is about learning how to crochet, it is a good example of what the correct side looks like.
http://crochet.about.com/od/crochets...c-stitches.htm
Could you post a close up pic of the outside edge of one of your crocheted doilies? If I can see them clearly, I can tell you if they are right side up.