This thread makes me think that I should write our name and number on everything outside!
It is possible that is our stern light. We lost one overnight after the Wolfeboro fireworks. Didn’t notice it was missing until the following Friday night when we were trying to head to the island after dark. As it was replaced it the next morning, we do not need it back. I had no idea that a stern light would float. Next time I will call MP, especially given how many times I have called to report found stuff myself.