Graffiti all around us

When you are walking around campus and in general, everywhere, besides conventional signs, there is graffiti. The restaurant next to Walgreen's has a large polar bear and a tiny penguin in the corner. I have no idea if it has been there since my freshman year or if it was added since I started school, but I'm fairly certain I did not see it immediately. Now I notice it each time I walk by because I think that it is such a cool piece of art. Once it caught my eye, I could not just walk by without looking at it. Another piece of graffiti that I have noticed is probably the funniest that I have ever seen. My family noticed it on move-in day freshman year when we were walking to ISR. If you walk from the Union to ISR, between Morrill Hall and Burrill Hall, there is one concrete "box", which is some kind of vent that sticks out of the ground. Across the street on the corner of Goodwin and Illinois, there is another vent/box as well. The one between the two buildings actually has stenciling on it which says "do not defecate." We thought it was really funny, not only because it specifically asks you not the "defecate" on that, in case someone were tempted (which I'm sure the sign was necessary to help people), but the one right across the street does not say anything, so is it ok to do it on that one?