This is particularly true if they’ve smoked marijuana, which has seen a resurgence in popularity among teens due to the push to legalize marijuana in some form almost everywhere in the United States.

So if you notice that your teen is driving much slower than usual, and he or she hasn’t had a recent accident that would warrant this behavior, keep your eyes open for other signs. Your child may be smoking a little reefer.

The car isn’t exactly parked quite right.

There are two types of sober teens: Teens who park considerately and teens who, well, don't. You know which category your normally teen falls into. That said, there are also teens that partook in various substances the night before and parked, well, as best they could.

In this instance, you’re not looking for the obvious car parked on the porch while the neighbors watch in horror. This impaired driving error will reflect something simple. Perhaps one tire is on the lawn. Or better yet, the car is in the garage but wedged so close to the wall that you’d have to climb in through the passenger’s seat just to get in.

If you see this, consider it a sign. But don’t jump to the conclusion that your child is definitely on drugs. It just might be a signal to watch them a little bit closer in case you see anything else.

A neat appearance has given way to complete insanity.

Only you know how your child normally looks. And if you’ve seen teenagers these days, you know that they can reflect a rather interesting fashion statement. The question to ask is: Has your teen’s taste in style changed considerably in a short period of time?