What do the skulls next to the crosses represent on the walker cards? If three hits (+++) take out a given walker, why are the skulls there?

I apologize if this has been answered before, or if it's clarified somewhere in the Revised Core Set rulebook (or if the question is too stupid).

Thanks in advance for the clarification.

Those cards are for Dust Tactics with slightly different rules. Don't worry about them while playing Dust Warfare. Search for Rodney's cards, available as downloads here in the forums for the cards with warfare rules.

Excellent -- thank you very much, Todosi. Will do!

I appreciate the help.