I've always assumed it's just art, or maybe an altered font. I do have a nice Illustrator trace of it, but can't imagine what font it may be derived from. I will check back here just in case someone else might know. I'd sure love to have that font!

I'd love to get the Barsoom font, actually.

Here's an example of A-Z in Martian (Barsoomian) text.

http://disney.go.com/johncarter/translator-share/#/translator-share/QSBCIEMgRCBFIEYgRyBIIEkgSiBLIEwgTSBOIE8gUCBRIFIgUyBUIFUgViBXIFggWSBa

Or a readable font that has the look of the Barsoomian letters.