Note the white wishbone C on the Bears helmet. 1973 was the first year with the outlined C.
Gridiron Garb: September 2014
Bears – Riddell NFL Pocket Pro Helmets
Chicago Bears Helmet - National Football League (NFL) - Chris Creamer's Sports Logos Page
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2015 Football Media Guide by Army West Point Athletics - Issuu
Chicago Bears: Take a look back at a century of uniforms
Chicago Bears: Take a look back at a century of uniforms
Chicago - HELMET HISTORY
Chicago Bears News: Team changes primary logo to a Bear – NBC Sports Chicago
Uni Watch Book Club: Best Plays of the Year, 1963