One of the best indicators that you are in a dream is if you can't read something that you are trying to read. For whatever reason, reading is impossible while dreaming and most people don't even have writing in their dreams to read. I do have writing in my dreams, but only rarely and am not able to read it. I've definitely used it to trigger lucid dreaming. I also use stuff like, "wait, how am I breathing under water?"

That's a common method people use to lucid dream. One thing I've read about is people making it a consistent habit to check their watch regularly while awake, so they eventually do it while asleep. Apparently clocks always look fucked up in dreams, so that's when they're able to figure out they're dreaming I guess?

But yeah, something about not being able to read text or a clock in a dream. Gets all weird.

I usually didn't either, but the (tedious) technique I used led to a lot more text in my dreams. I think because my subconscious was looking for them.

You have to spend a few weeks making this a habit: Every time you see a sign read it, look away, look back, and read it again. Once you've done that awake long enough it'll become a proper habit and it will carry through in to dreams. And in a dream when you look back the sign will be different - which will make you realize you're in a dream.