Final answer:
A white-lettered sign is typically a traffic regulatory sign, which is used to convey traffic laws and regulations to road users.
Step-by-step explanation:
A white-lettered sign is most commonly a traffic regulatory sign. Such signs are designed to inform road users of required actions, restrictions, or to provide notice of traffic laws or regulations. A traffic regulatory sign communicates the rules of the road, such as speed limits, no parking zones, and other traffic laws.
On the other hand, service/guide signs usually have blue or green backgrounds and provide directional information to services or points of interest, while route marker signs often are used to indicate route designations and bear different shapes and colors to identify the kind of route.
Lastly, warning signs are typically yellow and alert drivers to potential hazards or changes in roadway conditions ahead.