a lessons learned on gray man.. from a post on a similar thread, I had a situation in upcountry Thailand in 1973...the ability to blend in with local passengers on a baht bus was critical..
after the incident, I made changes to my off duty wardrobe to include..

shoes similar to population
tan pants, not Levi's
local print shirt
non logo ballcap

for an urban situation today, using public transportation or on foot, I would look to..

athletic shoes not associated with a gang
a gray "hoodie" or dark hooded wind breaker depending on season
dark ball cap without logo
wrap around sun glasses