Drivers encountering a do not enter sign must not enter the road, off-ramp, exit ramp, or crossover where the sign is posted. Do not enter signs usually indicate opposing traffic, meaning that the traffic will be coming towards the driver. Drivers must not enter the designated lane of traffic as there is a serious risk of collision.

DO NOT ENTER signs are usually installed at the beginning of one-way streets and ramps, often accompanied by a 'Wrong Way' sign. A Do Not Enter sign indicates that drivers are often going to encounter opposing traffic (traffic moving toward them, often at a high speed) if they enter contrary to the sign.