Seeing as though the marathon symbol also appears in Tau?
[url=http://en.wikipedia.org/wiki/Tau_%28Warhammer_40,000%29]See?[/url]
I just happened to pick up the Game Workshop strategy guide for the board game. Lucky too because i was going to toss it, not anymore though.
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If anything, it is the other way around. The Tau were introduced in 3rd Ed, in 2001. This is after Marathon began. Any similarities are likely coincidence.