Walking around the UW campus, one is constantly bombarded by advertisements for all sorts of things, ranging from the commercial (new restaurants, bar drink specials, coupon books) to the social (fraternities and sororities, intramural sports, student clubs of all sorts) to the religious (regular appearances by Mennonites, Hasidic Jews, and fire-and-brimstone Bible-thumpers) to the political (Democrats, Republicans, anti-war, pro-China, anti-China). These ads often appear in the form of flyers, picket signs, wearable sandwich-boards, banners, or good old-fashioned soapbox oration. By far the most prevalent (and least annoying, in my opinion) form of advertising on campus is chalking.
It is not uncommon, as I walk from the library or music building to the bus stop late at night, to see people carrying around buckets of brightly-colored sidewalk chalk, stopping every few feet to claim another blank area of pavement. These sorts of ads are usually fairly simple, owing to the necessarily one-at-a-time method of creation as well as to the ephemeral nature of chalk — indeed, of most things that are tramped upon by thousands of feet throughout the course of a day. Occasionally the chalking becomes more ambitious; a number of 20-foot wide peace symbols come to mind.
Near the end of the spring semester, I spotted what is definitely my favorite bit of chalking so far. It was done on the wall of a building, and parodies so well the style and tone of other more serious chalk advertisements:

