I haven't sat down and researched this but from what I have heard over the years about lucid dreaming is that you can't read in a dream. Reading is controlled by one side of the brain and dreaming by the other and supposably the two don't mix during a dream.
I have been having LD's for years, mostly unintentionally, but recently, I have been trying. Anyway, one night, I realized I was dreaming and thought about what I heard that people can't read in dreams. I tried it and it worked. I was only able to read two or three word phrases (they were on billboards along a road) but I did read and I was aware of the fact that I wasn't supposed to be able to read at the time.
There must be an exception to the rule because I have broken it. If anyone has done this too or can explain why I am able to read phrases in my dream, feel free to let me know.

Peanut Butter Jelly Time