Plenty of pics to be found in gawker, if you really need to see it. It's like every other crude scrawl you've seen on a bathroom wall. Frankly I wouldn't be so upset about the penis as how unoriginal it is. Pranks are supposed to be more creative than that.
To the high school senior: if all you can think of doing is putting a large penis on a football field, your high school education has failed you (and whatever college you were going to attend probably wouldn't make things better).