In the comic book Land of Black Gold originally drawn in 1939 but finished or redrawn some time in 1948 by the Belgian author Hergé (Georges Remi), one of the bad guys can apparently detect from the soles that a person is a police officer of sorts. Here is an excerpt from the comic in question, with the relevant setting:
The location is an oil tanker on its way to a fictional middle eastern kingdom. The man in the first panel is the "bad guy", and the man searching the drawer is Thomson, a Belgian detective, a fact unknown to the bad guy.
Since this is featured in a comic book, my guess is that it would be common knowledge for a teenager in 1939, but definitely not to me. My question is then, what is it actually he reacts to here?
Did the police back then always wear a certain type of shoes, or is it that every sailor had to wear special shoes, and the shoes he sees are instead "normal" shoes?