You'll usually see this phrased in a ticket, crash report, insurance letter, or a comment like, "The other driver was cited for failure to signal." It means a driver did not use a turn signal when the law or safe driving required one, usually before turning, changing lanes, pulling out, or moving in a way that could affect other traffic.

At a basic level, failure to signal is a traffic violation tied to communication on the road. Turn signals give other drivers, motorcyclists, bicyclists, and pedestrians notice about what a vehicle is about to do. When that notice is missing, even a routine lane change can turn into a rear-end crash, sideswipe, or intersection collision.

For an injury claim, that detail can matter a lot. A failure-to-signal citation may support an argument that a driver acted carelessly, though it does not automatically decide liability by itself. Insurers look at the full picture, including speed, following distance, road conditions, and whether anyone else also made a mistake.

In Montana, failure to signal can also affect comparative fault. Under Montana's modified comparative fault rule, Mont. Code Ann. § 27-1-702 (2023), an injured person can recover damages only if they were not more than 50% at fault. If an insurer argues that a driver failed to signal before a turn or lane change, that can reduce or even block recovery depending on how much blame gets assigned.