If you happen to come across a key chain with a medallion from East Hampton’s sesquarcentennial — that is, 350th — anniversary hanging alongside an ordinary brass door key and a Honda Civic ignition key, give me a call. For some reason, among all the items in my little old Coach shoulder bag when it went missing, the key chain’s loss is the most regrettable. It was a symbol of belonging, I guess. (And it’s not like you celebrate sesquarcentennials every day.)