This Tam o Shanter belonged to Charles McClaren who was a member of the Blairgowrie Home Guard during World War II.
The silver Black Watch badge is visible on the side. McLaren can be seen wearing the Tam o Shanter in the photograph of the Home Guard taken c.1941 (see below).
The form of Tam o Shanter worn during World War II was known as a General Service Cap. It is still is worn today by many Scottish military units as their battle headdress and the different regiment distinguish themselves by wearing different coloured hackles.

McLaren is pictured fifth from left.