Where are you located in Florida? The Germans did land saboteurs there during WWII. See the last paragraph. Possibly a discarded coin accidently brought ashore?
See exerpt below:
Operation Pastorius
Upon declaring war on the United States, Adolf Hitler ordered the remaining German saboteurs to wreak havoc on the country. The responsibility for carrying this out was given to German Intelligence (Abwehr). In June 1942, eight agents were recruited and divided into two teams: the first, commanded by George John Dasch, with Ernst Peter Burger, Heinrich Heinck and Richard Quirin; the second, under the command of Edward Kerling, with Hermann Neubauer, Werner Thiel and Herbert Haupt.
On June 12, 1942, the U-boat U-202 landed Dasch's team with explosives and plans at East Hampton, Long Island, New York.[4] Their mission was to destroy power plants at Niagara Falls and three Aluminum Company of America (ALCOA) factories in Illinois, Tennessee and New York. Dasch instead turned himself in to the FBI, providing them with a complete account of the planned mission, which led to the arrest of the entire team.
Kerling's team landed from U-584 at Ponte Vedra Beach (25 miles [40 km] south-east of Jacksonville, Florida), on June 17. They were tasked with laying mines in four areas: the Pennsylvania Railroad in Newark, New Jersey, canal sluices in both St. Louis and Cincinnati, and New York City's water supply pipes. The team made their way to Cincinnati, Ohio and split up, with two going to Chicago, Illinois and the others to New York. The Dasch confession led to the arrest of all of the men by July 10.