This may be weird but I can often tell someone's race (or ethnicity, if you like) just by their stature, walk, and general anatomy. Even from behind. I can't be the only one. I can often even tell the difference between various European people. Like certain body proportions I often see with Slavs, for example. North Africans, Africans, Asians? Completely different bone structure.

Pic 1: Boomercore
Pic 2: Glimpse of reality