Smoker's Signature
A Smoker's Signature is a way to tell if someone smokes but this method is not 100% accurate but it can be used as an indicator that someone smokes. 

The actual signature is that when a smoker sneezes they will not make much sound because their lungs can't hold in as much air as non-smokers can. Their lungs are often constricted as if they have asthma and therefore will not retain much air inhaled before they sneeze.
Jackie has a distinct Smoker's Signature, her sneezes are tiny compared to her swimmer friend.