From Dave Price

The horse at the left of this letterhead is so close to that on your RBBB poster that it is hard not to think one of them inspired the other (you would assume RBBB came first). Russell Pan Pacific was Art Concello's 1945 title but the Russell show had used the design as least as early as 1943. After Russell became the Beatty show, they also used this on letterheads but never on posters. What is the date of your poster? Does anyone out there have an earlier RBBB example of this image?