It's hard to tell unless you get really close especially if there is a case on it. I was at a party on Christmas and I still don't know if it was an iPhone 4 or a 5 that my friend was using. He was using Panorama mode but you can easily download a app on a iPhone 4/4s.
I see plenty of iPhone's in the wild but it's all a blur to me as a Note 2 user. People really notice a Note 2 when shooting pictures/video at a party even 15 feet away. Heck, talking on the phone is a attention grabber.
I bet when thieves in New York steal these from people they don't know which model their about to get. All that matters is that it's an iPhone.
As a long time Android user (wife loves her iPhone so I still come here) I'm really surprised to see a lot of S3's in the wild. It's very hard to compare S3 vs iPhone 5 numbers because it's near impossible to get an accurate reading when iPhone's look the same from a short distance. Do you really want to ask a stranger if their holding a iPhone 5 especially after all the robberies we hear in the news? Might end up in a police lineup because someone a block away got robbed.