from the FHWA site Shields and Signs:
- To mark the Interstate routes, the American Association of State Highway Officials (AASHO) asked its member States to submit suggestions. The States submitted dozens of ideas in several forms, ranging from a 55mm color transparency to a 4-foot square aluminum blank. AASHO's U.S. Route Numbering Subcommittee (Chairman Dewitt C. Greer, Texas; Rex M. Whitton, Missouri; James A. Anderson, Virginia; John O. Morton, New Hampshire) selected four for further consideration.
Full-size versions of the signs were erected on a road near the AASHO Road Test in LaSalle, Illinois, while a special meeting of AASHO's Committee on Administration was underway on August 14, 1957. State highway officials were able to observe the signs in daylight, dark, rain, and shine. The committee approved the final version, a combination of submissions from Missouri and Texas, on that same date.
On September 19, 1967, the U.S. Patent and Trademark Office issued Trademark Registration 835,635 for the shield. According to the American Association of State Highway and Transportation Officials, the trademark "has been used several times over the years to prevent or remove Interstate-like signs near the Interstate highways, where they might confuse the traveling public and cause accidents."
AASHO and Bureau of Public Roads (BPR) officials also had to decide what color to use for the Interstate guide signs. Federal Highway Administrator Bertram D. Tallamy of the BPR preferred blue, the color of the signs on the New York State Thruway he had helped to build as Chairman of the New York State Thruway Authority. Other officials preferred green.
To resolve the issue, the BPR, in cooperation with AASHO, staged a 2-week test on an unopened section of the Capital Beltway near Greenbelt, Maryland. Experimental signs were erected in blue, green, and black, some reflectorized, directing motorists to "Metropolis" and "Utopia." Hundreds of drivers-checked to be sure they were not colorblind-were recruited. With a recording official in the vehicle, each driver commented on the color, shape, and words on the signs. The recorder also noted when the driver noticed each sign.
The results were clear, with 58 percent picking the green background. The motorists preferred capitals-and-lower case letters over all-capitals, as well as reflective backgrounds. Tallamy approved the white-on-green design in January 1958.