Another Key West photo op is Mile Marker 0, at the junction of Fleming and Whitehead streets, is a small green sign that marks the southern tip of U.S. Highway 1, a full 2,390 miles from its northern terminus in Fort Kent, Maine.
The southern end of the 2377-mile (3825 km) long U.S. Highway 1 is in Key West. The highway begins in Maine at the Canadian border and travels along the east coast of the United States. This is mile marker 0 at the southern tip of the continental U.S.
Yes, this really is just a mile marker sign, just like the 100 or so others you've passed on your way down the Keys. Mile Marker 0 represents the end of the line, the furthest south you can get from the lower 48 continental states, and still be in the USA. It's the end of Highway One, which starts way up in Maine. So that is what makes it way cooler than all those other mile marker signs! :)
Mile marker zero is a tourist attraction only for those who enjoy seeing the obscure things and feel like your somewhere special. For most people it sounds silly to say you stood on the southern most point in the US (same applies to the four courners of the southwestern states attraction) but it provides a nice photo op to send to your friends.
US 1 begins (or ends) in Key West on Whitehead St. It is almost 2400 miles long and runs through 14 states and D.C. The other end is in Fort Kent, Maine. It was started in 1926. The sign is often stolen by souvenir hunters.
Your just walking down the street and here is this marker for US 1 hanging on a lightpole. Not anything interesting just thought I would put it up.