There are a few ways to spot an Australian in a crowd.
One is to look for the cheeky type terrorising the locals at the bar with tales of drop bears or some such lark. My dad, for instance, who spent a few misguided years in the military as a younger man, will gleefully regale anyone who will listen with the time he sold an unwitting American recruit a genuine Kangaroo tail feather one afternoon on exercise. (It only looked like a magpie feather, the young patriot was assured before he happily parted with his money and made off with the rare find. Bless.)