alt Hacker NewsMy tell is to recognize any room with a piano in it. I naturally want to sit down and play this piano, but the keys are totally wrong. No problem, I'll look around and, lo and behold, dozens more pianos all... with the keys in the wrong places. I can't play anything. "Oh, this again. I must be dreaming. How frustrating."
A very regularly occuring dream is that I'm in a train and realize that I don't have a ticket (never happened IRL), so I want to buy an e-ticket, but the ticketing app does not work. The text changes all the time, the buttons move around, weird errors, and then I realize 'yep I'm in a dream again'.
The nicer lucid dreams are those were you can fly or make spectacular light and colors, but I find that it's usually a difficult balance to avoid waking up.