User blog comment:JokerJay779/I want you! To make E-100 Series robots!/@comment-4861962-20141002202604/@comment-4861962-20141003001918

Sigma does have weapons, as mentioned in the last paragraph. Mostly for self-defense, as it relies on its networked robots for actual combat. Sigma itself is -very- damage resistant, albeit slow, and is very physically strong.

Its appearance is meant to reflect its purpose as a computing device rather than strictly a war machine. (I meant to write this in more detail, but ran out of time, hence why the sentence just trails off at "the chest.") The closest thing that resembles what I had in mind is a Warhammer 40k Castellax, which come to think of it, actually looks pretty close to an E-100:

http://img4.wikia.nocookie.net/__cb20140506211657/warhammer40k/images/4/4c/Castellax_Class_Battle-Automata_Omega-Pi-Seven.jpg

Something like taht, with a chrome/black color scheme, an antenna over its left shoulder, and standard E-100 head and other accesories.