This is an interesting one, marked 'Guard's Loaner' and the seller told me it was the loaner for a jewelry store when repairs were being done to the customer's watch. I'm not sure where the 'Guard' part comes in, unless the store was called 'Guard's' or maybe it was for the Security who watched the store?
Anyway, top drawer construction throughout with cap jewels and Breguet Overcoil. Running strong now with her new mainspring and full service. The seller thought it might be a Caldwell.