A bell-boy hat or bellboy cap is a small round or oval brimless cap with a crown about 2–3 inches in height, resembling a squat can or drum. It is often worn as part of the uniform of a bellhop

Bellhop

A bellhop, also bellboy or bellman, is a hotel porter, who helps patrons with their luggage while checking in or out. Bellhops often wear a uniform , like certain other page boys or doormen...

. The bell-boy hat is based on a 19th century military drummer boy's cap. A bell-boy hat usually features a chinstrap, and is trimmed to match the rest of a bellhop's uniform. It was often worn at a rakish angle and was popular in the late 1930s and 1940s for women, when it could be dressed up with veils, military trimmings or a snood

Snood (headgear)

A snood is historically a type of European female headgear, or in modern times a tubular neck scarf. In the most common form the headgear resembles a close-fitting hood worn over the back of the head...

(a decorative hairnet). The chinstrap would then be worn to the back – under the skull – to help secure it to the head.