My sister is a cocaine addict and I can generally tell by her voice when she’s done coke, but other ways of noticing would be if they smoke they tend to smoke more than usual, won’t want to eat or very little as suppresses the appetite, drinks plenty of booze normally drink like a fish on coke , rambles, paranoid, jumpy. No eye contact, Bank/credit cards might have coke residue in the numbers of the card. Some people just use a car key to scoop it up and snort it.
The next day sleeping a lot and v irritable and snappy xx