Conn 50M, made at the Best Manufacturing facility in Nogales, Arizona (Conn USA, not Conn Elkhart).  It is identical to the Vito "Kenosha" Model 38, which was in production at the facility at the time Conn acquired it circa 1960.  The oddball serial number is within the Vito, not Conn, sequence, so it is probably a very early example.  Production of the Model 38 continued with some units branded "Conn" and others branded "Vito."  

The 14M and 16M models were produced in Nogales along with the 50M starting in 1963.  The 50M, 14M, and 16M are all referred to as "Director" horns and have the same shooting star engraving, which is no doubt a source of confusion.  So if you're ever looking for another one like yours, you're at least as likely to find one looking at Vitos as you are looking at other Conns.  

Here's a link to a site with comparison photos of the Vito Model 38, Conn 50M, and Conn 14M.

http://doctorsax.biz/vito_conn.htm