Because some kind soul was asking for it, Marko explains the Writer’s Bump:
The Writer’s Bump is a little callus on the middle finger of the writing hand of someone who writes with a pen a lot. As people have largely switched to computers for composition, the Writer’s Bump has gradually been replaced by new professional trademarks: the Writer’s Carpal Tunnel Syndrome, and the Writer’s Extra Thirty Pounds From Sitting On One’s Ass Near A Fridge All Day Long.
I must point out here that my desk and my fridge are more or less in opposite corners of the house. Then again, no one’s likely to accuse me of being a writer, either.