Read a page of text, then read it again to see if it changed. This test never seems to fail, at least in the sort of dreams I can remember having after waking up. Usually I can't read at all in dreams, and when I can, the text is different every time I read it.
I thought this was just me! There have been times when I've "read" in dreams (signs, usually), but I don't actually visualize the words. I just "know" what they say.
