This is the 5653rd most frequent Russian word.
предупреждает
"Warns" or "alerts."
Here, "предупреждает" means 'warns' and is used to indicate that someone is providing a warning or alert about something.
Он предупреждает нас о возможной опасности.
He warns us about a possible danger.
In this case, "предупреждает" functions to highlight that a sign serves the purpose of notifying drivers of a condition or situation.
Этот знак предупреждает водителей о ремонте дороги.
This sign warns drivers about road maintenance.
Here, "предупреждает" has a didactic undertone, being used by a professional to convey an important precaution or advice.