"That's a dragoon's moustache. He served in the cavalry regiment."

German military officer
Creative Commons Attribution Share AlikeGerman military officer - Credit: quinet
By the beginning of the 18th century, 'dragoon' -- which had originally denoted heavily armed cavalrymen -- had become the standard term for those military units trained to fight either mounted or on foot. As such, they existed throughout the majority of European armies. Certainly in British circles at the time of World War I, the size of one's moustache -- something which became linked to military tradition -- was thought to be directly correspondent to the position of rank.