Remember that stupid "S" symbol we kept drawing in early grade school?  Well, now you can spray it on walls in any Source game, in addition to asking the question, "WTF IS THIS STUPID THING ANYWAY?!"

Just extract and install via the options menu plox.  kthxbye.

P.S.
I've also included the SVG file for editing.  Just open up in the vector drawing program of your choice.  I claim absolutely no credit to this thing, since that symbol definitely wasn't my invention.