write "Are you dreaming?" down on the side your index finger. That way whenever you are looking at your hand, or even just something in/near your hand you'll remember to do a reality check. Then you look at your watch (or the nearest clock) and do a reality check.

It also looks pretty cool when you make a fist, because it says "are you dreaming?" and it's wrapped around in a spiral.

What other methods do people use to remind them to do reality checks throughout the day?