A square or rectangular white sign with black text typically indicates:

Black-on-white rectangular signs are regulatory: they communicate rules drivers must obey. Examples include speed limits, no parking, one-way arrows, do not enter, no turn on red, and lane use restrictions. Disobeying a regulatory sign is a traffic violation. Warning signs are typically yellow diamond-shaped; guide signs are usually green (route information), blue (services), or brown (recreational and cultural). Construction signs are orange. Color and shape carry meaning, so a driver should be able to identify the category of sign at a glance even without reading the specific text. The MUTCD specifies these standards so signs work consistently across all 50 states.