If I had to estimate "common and noticeable" sightings based on our old office near twitter and my experiences: Homelessness -- multiple per block Excrement -

If I had to estimate "common and noticeable" sightings based on our old office near twitter and my experiences: Homelessness -- multiple per block Excrement -- every other block Public drug use (non pot) -- every other day Public urination -- once per week Public defecation -- once per month I was assaulted at the street corner near our office once in the 1.5 years we were there. My guess is that the homeless population is just too large to manage any reasonable degree of cleanliness.