Look into all day awareness. It's the phenomenon of noticing the incredible level of detail of the real world and trying to do that all day.

Checking clocks for consistency. Text as well. They are less reliable. Some people swear by rotating a text containing object upside down and see if the text auto-rotates, apparently it does in their dreams. Some people can't read anything in their dreams.

Read something, and then read it a second time. If you are awake it will be the same text, but if you are dreaming it will have changed.