started life as sew on cloth badges embroidered with a letter or letters
to indicate the particular trade.
Proficiency badges of WW1 & WW2
Later the move was made to metal
badges, often with a backing plate that went inside the sleeve, to
indicate the same thing.
As a generalisation these were peace
time badges. Those that were worn in wartime were not often worn in the
field on combat uniforms.
Over the years they were produced in
different fonts, different styles and different metals, as this grouping
of LG (for Lewis Gunner originally and later for Light Machine Gunner)