There is a 9-part documentary about Chuck Jones available on YouTube, which in several places shows him using a Blackwing 602. This first still comes from the final segment of the film.

Here is another picture, Blackwing in-hand:

There is also an interview he did with Charlie Rose where he demonstrates some techniques:

At one point, Charlie asks him about his “pen”. Chuck gently corrects him, stating that he has a pencil. He adds: “A pen is full of ink. This [pencil] is full of ideas.” Sounds like a great tag-line or motto for a pencil…