The thing with the sign has never happened to me.. though, in one of my first lucid dreams, my friend told me I was dreaming, after I asked.. o_o Which was odd.

Me, standing in a weird block-place: Is this a dream?
Friend: Yup.
Me: o_o

Then, I went and talked to some DCs of people IRL.. And me and my friend went back to the begining, and I tried to fly.. And failed.. then woke up into another dream, in a classroom, with the bell ringing. o_o

I wish that I'd be able to have things like that in a dream.. That'd be cool. xD