Back in the 1940s, Fawcett Publications kicked off one of the most endearing fan clubs ever devoted to a four-color super-hero. By sending 10¢ to Fawcett's corporate headquarters, the Big Red Cheese's readers could become a member in good standing of the CAPTAIN MARVEL CLUB. One of the premiums that shipped with club package was the CAPTAIN MARVEL CLUB MEMBERSHIP CARD (seen below). And no mere membership card was it — because by flipping it over the now initiated club members were not only given the ability to create their own secret messages but, more importantly, they were able to decode the messages Cap had left for them in the issues of CAPTAIN MARVEL ADVENTURES.

A Message from Cap!
SVB KZO, DVOXLNV ZYLZIW! KOVZHV SLMLI NB XLWV YB HVMWRMT LMOB DSLOVHLNV NVHHZTVH ZXILHH GSV RMGVIMVG.

Type or copy your Code Message below and

Type or copy your True Message here and

Writer/Artist Jeff Smith made use of Captain Marvel's secret code in his 4 issue prestige mini-series SHAZAM!: THE MONSTER SOCIETY OF EVIL. In each of the four issues, Jeff encoded both the chapter titles and the title of the subsequent issue. DC Comics' supported the series with an Adobe Flash version of the decoder so that readers could easily decode the titles. The decoder was available on the solicitation page for each issue but sadly, DC allows the solicitations to roll off its site after 4 months of release, so there's no direct link to the decoder on the site. It's still out there though, so here's DC's version of the decoder:

Here's hoping that Mike Kunkel's BILLY BATSON AND THE MAGIC OF SHAZAM!
makes liberal use of Cap's secret code!