There is a look. Even on guys with not much muscle, the skin gets a look and texture that a seasoned juicer/gym goer can see.
Saying that someone can come off and hold a lot of muscle without that look. I remember when i was clean for 5-6 months people still thought i was on.
But i've seen clean-for-life guys who most people on the street would say was on gear, and i've seen plenty of gear uses who look like rubbish. Only when you know the look can you tell the difference.