Highway route marker or guidance sign.
It depends on your state. Most are black and white but vary in shape, Calfornia has a green state highway sign.
loop 270
A road sign indicating a state highway generally has a unique design for each state. In South Dakota, the symbol of the road is outlined with borders of the state.
There are different types of highway signs. The type of sign that would let you know that you were on a short state highway in a city or urban area would be a rectangle sign with black writing.
White square with black text. Usually has a word like "loop" and then a number on it.
A vertical Rectangle that will have the word Loop and it's number. And example is on 5-16 of Texas Drivers Handbook that says LOOP 270
state
Actually, the KKK didn't name the highway after Rosa Parks. The state of Missouri did. They did this because one of the participants in the KKK wanted to participate in the 'adopt a highway' thing, but Missouri said no, and the KKK took it to court and the court said it was unconstitutional not to give the highway to the KKK. BUTT, the state of Missouri found a loophole so that THEY could name the highway. So, in short, the state of Missouri named the highway, not the KKK (Ku Klux Klan). -Unipegutato
A state highway is a road that is either numbered by its state with a number that is lower than U. S. national highway routes, or a road that is a U. S. national highway route, but is maintained by the state in which it is located.
The prefixes for state highways can vary by state, but common ones include "SR" for State Route, "MN" for Minnesota State Highway, "NY" for New York State Route, and "TX" for Texas State Highway.
Ohio State Highway Patrol was created in 1933.
Texas State Highway OSR was created in 1942.