Mate, it's those diagonal/zig-zag lines that are embroidered on officer's shirt collars, and they also appear on the cuffs of coats and the band around the czapska. I've got a photo of my grand uncle from, it appears, the 1920's, with just a solid embroidered zig zag line on his collar, whereas my other grand uncle's and dziadeck's collars (pics from just before WW2) show the zig zag but as a thicker 'bar', with other zig zaggy lines inside the border. I'm not very computer savvy so I don't know how to post a picture. Cheers mate.
PS - I'm not talking about chevrons which appear on the arm of a shirt.
Generally speaking, diagonal stripes are given for two reasons, a certain duration of active duty, such as one stripe for every three years; and also for service spent out-of country.
Thanks Jason. They seem to have commenced in the late 18th Century, and particularly around the time of the Napoleonic Wars. Any idea as to why they are shown as squiggly lines, and where the idea came from?