I am starting a new topic for postcard signs today. I am planning to include postcards of all types of outdoor signs. Most, but not all, will be chrome postcards of roadside signs: highway signs, billboards, historical markers, welcome signs, advertising signs, etc.
I have been accumulating these cards for many years. Most have been found when I am not really looking for them. Postcard dealers are unlikely to have a signs topic — most dealers don't even have a roadside category.
U.S. Route 1 seems like a good place to start. Here is some information on U.S. Route 1 and Florida signs from Wikipedia:
U.S. Route 1 (also called U.S. Highway 1, and abbreviated US 1) is a United States highway which parallels the east coast of the United States. It runs 2,390 miles (3,846 km) from Key West, Florida in the south, to Fort Kent, Maine at the Canadian border in the north. US 1 generally parallels Interstate 95, though it is significantly farther inland (west) between Jacksonville, Florida and Petersburg, Virginia. It connects the major cities of the east coast, including: Miami, Florida; Jacksonville, Florida; Columbia, South Carolina; Raleigh, North Carolina; Richmond, Virginia; Washington, DC; Baltimore,Maryland; Philadelphia, Pennsylvania; New York, New York; New Haven, Connecticut; Providence, Rhode Island; Boston, Massachusetts and Portland, Maine.
In Florida, where signs for U.S. Highways formerly had different colors for each highway, the "shield" for US 1 was red. Florida began using the colored shields in 1956, but during the 1980s the MUTCD was revised to specify only a black and white color scheme for U.S. Highway shields. As such, Federal funds were no longer available to maintain the colored signs. On August 27, 1993, the decision was made to no longer produce colored signs. Since then, the remaining colored signs have gradually been replaced by black-and-white signs; at present, there are a few rare colored ones still in place.