In addition to carrying for practical purposes, handkerchiefs have long been displayed in the top pocket of men's jackets. Used in this way, they are referred to as a

pocket handkerchief


pocket square

. A traditional pocket square will have the hem rolled, contrary to handkerchiefs.
The trend of pocket squares as a fashion accessory really started during the 1920s, and was considered a trendy accessory up until the 1960s, where actors such as Cary Grant, Fred Astaire or Gary Cooper used to wear them regularly. It fell into disuse up until the 1990s when the pocket square made a comeback thanks in part to popular television shows such as Mad Men.
Pocket squares are usually made in fabrics such as silk, cotton, linen or wool.