Will Eisner uses MSG Half-Mast and Connie to explain PS Magazine's purpose.
From Army Information Digest, Apr 1964.
What's an explainer, you ask?
The term actually defines itself: it's a form of communication intended to explain something. In the case of PS Magazine
—or as it was called at the outset, PS: The Preventive Maintenance Monthly
—the chief purpose of the cartoon-illustrated bulletin was to explain how to care for vehicles and equipment. Its genius was the marriage of sequential art (cartooning) with conversational explanations by its creator, Will Eisner, to convey technical information in a way that facilitated comprehension and retention.
To honor the magazine's 70th anniversary, professor and librarian at the University of Nebraska-Lincoln, Richard Graham, wrote "A Brief History of One of the Original Explainers: PS, The Preventive Maintenance Monthly
" for The Comics Journal
(click the title to hyperlink to and read his article).
In addition to serving as a member of the UNL faculty, Graham is managing editor for SANE Journal, an open-access and peer-reviewed periodical dedicated to using comics in the classroom. He has been an Eisner Awards judge (2015) and nominee (2012) and is the author of Government Issue: Comics for the People, 1940s-2000s.