Final answer:
Railroad crossing signs are round signs that indicate upcoming railroad crossings and alert drivers to be cautious and prepared to stop if necessary.
Step-by-step explanation:
The round signs you are referring to are actually called railroad crossing signs. These signs are used to indicate upcoming railway crossings and alert drivers to be cautious and prepared to stop if necessary.
They are usually yellow with a black symbol of a train on the tracks. The purpose of these signs is to ensure the safety of both drivers and pedestrians by providing advance warning of a railroad crossing.