Gee, thanks for asking.

Spectators hold up clever signs.  I've seen ones saying "Run Like You've Stolen Something" or "Run? I Thought You Said Run".  Here are some held up near the start of the 2013 Soldier Field 10 Mile Race.

I know they're too far away to be seen in this photo, but the one that caught my attention was "Have You Pooped Yet?"

This next photo, by the way, is not the line to the portajohns.  It's my view from the start.  People were assigned to corrals, and were started in segments.  "Wave starts", they call them.