this totally differs from person to person and depends on the situation as well

common signs i can think of that i have seen in myself or others, signs that i always try to hide or avoid:

- obviously red eyes,
- your upper eyelids may drop a bit
- my eyes look glossy when high, almost like someone has sprayed a thin layer of cooking oil on them, no matter how much eyedrops i use, the glossyness doesnt go away
- Mumbling when talking . lower than usual voice (like when u catch a cold)
- In certain occasions your tongue will look whitish aka "cotton mouth"
- slow reaction times
- Slouching posture
- altered walking, partial lack of balance
- Paranoia --> bad judgments

I for one have had control over all of the above, except for the voice, i will have to talk louder, cuz naturally your vocal cords apparently get thicker and thus produce a lower voice due to less vibration.

and as for the last one, dumb people fall into the 2nd part of it. a 2 car convoy of me and my friends were moving household stuff to my friends new apartment and there were buncha people i didnt know personally in my car who were among the moving team. the u-haul got pulled over, my friend driving it sober didnt have his license on him, we stopped a bit further on the road with cops flash light fixed on us, the people in the car were freakin out, i told them to turn off the blunt and put it into my hiding spot and told them not to move around too much and just relax. I got out high as hell-thankfully got few secs to refresh my eyes and put some cologne on + a gum- and just acted as str8 as i could and went up there and talked to the officer as nicely as possible and explained to him the situation, he let my friend go with a citation and didnt even bother to come check us.

later i figured one of those fuckers in my car wanted to so stupidly screw us all by gettin out and runnin into darkness. i never ever saw his face again.

point being: these are not applicable to everyone.
high confidence and quick/good thinking, can cover your ass, even if u look totally blown into a different dimension!!! there are plenty of situations where u can have symptoms of apparent high and not be high, like sickness or tiredness after work or allergies. the normal (not a nazi one) cop will buy your story based on how u act n how confident u r.