In Downtown LA there are not many places to relieve yourself if you are not a paying customer. If you are homeless and roaming 6th Street and suddenly hear nature calling, you can't just use the public restrooms provided by the city, as there are none. There is no reason you can't just squat down and take a crap on the sidewalk, well no reason other than human decency and/or self-respect.
Just in case you didn't realize that you could use the street as your own personal toilet, local artist Richard McDowell[via blogdowntown] has made wonderful signs that let you know you can. Don't forget to Bring Your Own Paper. According to the rumors on blogdowntown, the signs are part of a film that the artist is making. There are also drugrelated signs in case you have trouble finding a drug dealer in Downtown.
I didn't mention it, but there are actually portapotties a few blocks to the southeast on 6th.