Actually the sticker and bandanna were free. The crazy Maoist group World Can't Wait worked with the Berkley High School (big surprise there) and the kids were given the day off school if they went to take part. Two groups were giving away the "Make Out, Not War" stickers and free T-shirts and bandannas to the high school kids. Here is a great read (kind of long) with lots of pictures detailing the protest and exposing what a bunch of bs it was.
https://www.zombietime.com/berkeley_marines_2-12-2008/