Here, it's legal for folks to be publicly naked as long as they're not causing a total ruckus. I've learned to identify nude passersby from far away, which allows me the good fortune of averting my eyes early on...
Here's what to look for so you don't have to look!!
a) a far-away pedestrian who seems to be all one fleshy color
between the neck and ankles.
If you suspect (a) to be true, verify your findings by consulting (b)
b) Look for a space-cushion radius of 3-6 feet around suspected
naked-person (because no one wants to walk super close to the
naked guy in tennis shoes).
If you find (a) and (b) to be true, I recommend wasting no time and quickly activating the being-really-interested-in-your-phone-technique or the suddenly-very-turned-around-and-looking-up-at-all-the-street-signs (with squinty/confusion-filled-eyes to make it believable) approach until the coast is clear!
. . .
p.s. I know that many places on earth have nudists besides San Francisco. My chart is just meant for funny's sake.