Taxis are easy to identify - cars with a (usually lit) topper and writing all over them are taxis, the writing doesn't even have to be in a language you understand to be identifiable as a taxi - you don't need to actually be able to read the writing. Other marks like checkered patterns are common, taxis are designed to stand out.
New York City also has green taxis, so it's not anywhere-centric thing.
I mean you tell me to check the markings, but you know in those captchas you can't see any markings because most things look like a blurry blob.