which us city has a post office that doesn't fly the american flag

The post office you’re asking about is the B. Free Franklin Post Office in Philadelphia, Pennsylvania. It is famously reported as the only post office in the United States that does not fly the American flag, because it recreates a colonial-era post office and was established to reflect the period before the United States flag existed. It also does not use a ZIP code, aligning with Franklin-era postal practices. If you’re curious about this site, it’s part of Independence National Historical Park and operates as a small museum as well as a functioning post office.