Unless this doctor really wants you to smash into him (and I'm pretty sure it belongs to a guy because I saw a dude in the store wearing scrubs - totally what a guy with this license plate would do), there's really no reason to do this.
Can you imagine what the roads would look like if everyone had their profession on their car's bumpers? It would make it easier to find, say, a dog walker or a landscaper. But do people who have REAL dirty jobs do this? Is there an abbreviation for sewer cleaner or people who do colonics? Never mind. I don't want to know.
I just hope if I run into El Doc again, it's when I'm feeling extra hypochondriac-y. He can't run from me! He put his doctorness out in the universe! He WANTS to help