Most likely it's Mil-Comm TW25B, Sig's grease of choice. I don't think it contains any lithium.
http://www.mil-comm.com/index.php?op...&id=46&Itemid=
http://mil-comm.com/images/stories/p...TW25B-MSDS.pdf
It does, however, use "PTFE nano-particle technology" and "penetrates the pores of metal surfaces."