I can’t do the jumping up to see if I’ll fly in public. Even looking at my hands draws attention. 
Have a watch on your arm, and look at it.
Then look at it again.
One that i like is thinking: ‘If this is a dream, there will be a red car/yellow bike/apple tree etc behind the next corner’ ‘If this is a dream, that car will start flying/that house will grow/a cat will fall from the sky etc.’
Nobody can see what we think. 
Grab your nose and try to breath. Always worked for me. And unless you are with friends or people you know you can do anything, people dont give a damn. Well not around here.
Try to remember when you woke up, or reflect upon what has been going on or is going on right now, while judging whether it might be a dream. That is quite undetectable to other people.
You could try asking yourself some questions above your environment:
Where am I?
Why am I here?
Is anything strange or out of place?
Who is with me?
It’s all about carrying an awareness with you throughout the day. The best thing is that you can do it anywhere without looking silly 
What I do is bite my thumb. It works and doesn’t draw attention if you look like you are focusing on something else.
Try to push your finger through your palm hard…No one will pay attention to that…except everyone around hmm…
Now for real…You should do mental RCs, like someone above suggested.You don’t have to search for mental RCs, you create one yourself.
There are MANY ways you could check if you are in a dream…Use your imagination, use your mind!
You can try using the nose reality check. Simply close one eye and try to see your nose. If you can’t see it, then you are dreaming.
Cos that doesn’t look weird. Myself I do the nose RC very discretely like I have a cold- Looks like a snuffle. Also, looking at your hand will not make you seem weird- A bit vain perhaps, but not weird.
For me, nose-pinch is all that works for sure during a dream, however, mom thinks it is ignorant, and recently she started saying “this is not a dream” everytime I do it, so, when I do it in dreams, it is becoming slowly less effective, becuase all the DC’s simaltaniously say “This is not a dream” and I lose lucidity…
Anything mom won’t notice?
“This is not a dream!”
“Well then you might wanna call the circus cos I’m breathing with my nose and mouth closed”
Lol, make the phrase “This is not a dream” like an RC cue - Let it trigger yet another one, like counting your fingers.
I tried this in the last lucid dream I had. I imagined that it would start raining oranges. Within a second I was showered by the fruit and fully lucid 
Anything with numbers, writing, or a digital display will rarely appear as it should in a dream. If you have a watch or mobile on you, they will both work nicely. If you already suspect you’re dreaming, you can simply imagine you have these items so that you don’t have to go searching for them.