They sneak out at night to work, cover their faces from view, and often use pseudonyms "just in case."
But while street artists may prefer to see themselves as on the fringes of society, the pictures they create, and many of the big names creating them, are now very much part of the mainstream.
Names such as Banksy, Blek Le Rat and Shepard Fairey are commanding big money. And they have become celebrities in the time it used to take for an artist to find a gallery willing to host a debut show. So it should be no surprise that street art is driving major change in the way art is sold around the world.
When your original motivation for picking up a spray can is about breaking away from convention and sharing - be it on the side of a bus or in a dimly-lit subway - the traditional model of giving up half of your earnings to an agent and gallery owner seems a little out of date.
Increasingly artists are seeking a new way to sell. A new generation of talent - brought up with the freedoms of the internet - is threatening to tear down the traditional route to the art market, which involves a whole host of intermediaries taking a slice of the action, in favour of more direct action.
That's where we've come in. Up until a couple of years ago most art dealers and collectors would know Dreweatts as a fairly traditional auction house - all very Antiques Roadshow, dark wood panelling and experts in tweed, you know the kind of thing.
The vast bulk of our activity is selling stuff for individuals and dealers, and still remains so. But in the world of urban and contemporary art, we've started to do stuff differently.
Back in September 2008 Damien Hirst shook up the art world by selling an entire collection by auction at Sotheby's. But three months earlier we ran our first Urban and Contemporary auction, taking much of the work for sale straight from the artists.
It's not difficult to see why selling via auction is an attractive option. Ask artists how they best like to spend their time and the answer will be getting their hands dirty working - not getting their hands dirty dealing with sales and marketing.
My job is very much as a talent spotter and shop-keeper for current artists. Over the last three years our sales have gained an international reputation among collectors, allowing artists to build an international profile much quicker than they might by exhibiting at a local gallery. The fact that an auction house typically takes a commission of around 15% of the sale price is another real positive in our favour.
Of course, it hasn't gone down well with many of the establishment's old guard. Traditionalist agents and gallery bosses dislike the direct-sell tactic believing it cuts them out of the picture [no pun intended].
Some also claim that auctions deflate prices, since they cut out the need for the necessary mark-up they would normally take. That's something we can't argue with, though many of the artists are pleased the work they create is, for the first time, being sold at its 'real' worth, as judged by the market. In many cases this can be much higher than expected too, especially when bidders battle over a piece in the sale room.
By selling via specialist auctions, artists know they are getting in front of serious collectors as well as casual buyers. For new talent, such as Portuguese painter Maria Imaginário, being included in a catalogue alongside big names like Banksy is a PR dream, catapulting her work to a whole new level.
This direct approach is still in its infancy, though the fact that forward-thinking galleries and agents are now working closely with us to promote artists suggests things are changing for good. Only recently, the Other Art Fair at London's OxO Tower showed how artists were taking charge of their brands by selling direct to the public in a collaborative way.
Who could have imagined that urban art, born out of the secretive and hidden world of graffiti, is bringing transparency to the art world?
Dreweatts latest online auction, Urban Editions, features 148 lots including artists such as Banksy, Antony Micallef and Nick Walker, with prices from just £80. Perfect as a Christmas gift or for budding art collectors. Bidding closes on December 6. See http://www.i-bidder.com/en-gb/auction-catalogues/dreweatts/catalogue-id-2413