Nine digit code used by the Unabomber in his correspondence with the media and law enforcement. Such codes are typically used by criminals and terrorists so the authenticity of their messages can be verified. The code is kept secret from the public, of course.

This particular code is the social security number of a petty criminal from California. That man has a tattoo that says "pure wood". Probably a coincidence or a false trail planned by the Unabomber.