I've gotten some comments on my BOB when the trunk of my car is open. Mine is a Camelbak in hunter's camo -- I would have preferred something less attention-getting in urban environments but it was on closeout.

Note that in addition to active signalling gear I have a large blaze orange bandanna in my BOB if I want to be more visible.

In urban environments I work hard to be discreet. Weapons and tools are concealed. My "stuck on a train" kit is kept in separate pockets from everything else in my laptop bag. Dark, muted colors are the rule. I'm glad to talk prepping with friends but I err on the side of caution with strangers. That means keeping things under wraps.

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
backpack

The only thing I wonder about are things like the G20 and Occupy movements. This attire sounds a little like the black-whatever-they're-called that ramped things up there. Dark clothes could be mistaken by the police as the clothes of a professional, radical protester. I'm more inclined to go with earth-toned browns and greens.

That said, the older I get, the less inclined I am to spend time in cities, especially big ones. I like to hope that, with this in mind, if the worst does happen, I'll want to be found not camoflauged.

All that said, my trunk's loaded with gear that's kept out of sigh unlese the trunk is open. If anyone does ask about it or the bag under my desk, a great answer is "I'm a Scout Leader."

Big cities have all kinds of people dressed all kinds of ways, all the time. Unless you're streaking naked, dressed like a street-walking prostitute or wearing a professional sports uniform in DC, you're unlikely to stand out.

Anyone who has gotten a glimpse into my ample car gear knows that I'm an outdoors enthusiast (i.e. backpack, boots, hiking poles, paracord...) and like to be self-sufficient in regards to basics like tire air compressor, jumper cables, etc.

No one has shown a propensity to rifle through my stuff. If they did, they would not get a second opportunity.

Get one of those nondescript military blankets and keep it over your gear bags, tuck the edges under. If you need the bags, just toss the blanket aside.

Sue

Car stereo installers have gotten quite creative at building false floors or dividers. If you have a false seat back or false floor (in the trunk) covered with the appropriate automotive carpet almost no one is going to notice unless they are looking for it.

You can get a fair amount of stuff in a 4-6" false floor or a 12-15" false seat back.

A cheap, large, nondescript duffel bag without any exciting logos will conceal a lot of stuff too. If you have kids in sports like I do we always have several extra duffel bags laying around collecting dust.

A black fleece blanket ( or scrap) over whatever is visible in your seats/trunk makes them nearly invisible. Also, remove your GPS and GPS mount.

That's largely true in "downtown" areas but much less so in residential neighborhoods, such as you might be walking through to get home.

I like storing things in coolers for a low profile. Big cooler in the car or a lunch-sized one at my desk. A beat-up cardboard box, especially if labelled something like "books to donate" is good for the car too.

+1 on the cooler. Water/ dust proof. sturdy and soooo common and boring.