“I think the message here is that, if you do see a piece of graffiti art out there, leave it, leave it for the public,” Maas said in a manner reminiscent of a not-angry-but-disappointed dad. “I’m not lecturing you. I’m just saying, without that certificate, it’s just very difficult to sell. With it, it might be worth £20,000. Without it, you’re nowhere.” – Artnet