Meaning of 'on a reader'

Question

What does reader mean here? I simply can't find a proper meaning for this anywhere in dictionaries.

There was something about Jerry's face that worried me. As if I had seen him before, but not very lately, or in a newspaper photo.
...
"I've seen him somewhere. Maybe on a reader."

_{From Raymond Chandler's "The man who liked dogs" (1936)}

Answer 1

It's a wanted poster:

U.S. colloq. A police circular identifying a wanted person; a ‘wanted’ poster.
_www.oed.com

According to the Oxford Dictionary of Modern Slang, it was used between 1922 and 1955 (which explains why it's not in most dictionaries).