Just for decoration. It used to be common to hang a fob from a pocket watch chain (in my case a smartphone chain 🤓)
“Chains were frequently decorated with a silver or enamel pendant, often carrying the arms of some club or society, which by association also became known as a fob.”
https://en.wikipedia.org/wiki/Pocket_watch
What do you use the moon for?
Just for decoration. It used to be common to hang a fob from a pocket watch chain (in my case a smartphone chain 🤓)
“Chains were frequently decorated with a silver or enamel pendant, often carrying the arms of some club or society, which by association also became known as a fob.” https://en.wikipedia.org/wiki/Pocket_watch
See also: https://en.wikipedia.org/wiki/Cigar_cutter_watch_fob