Usually printed on a t-shirt to get someone to ask what it means. Referenced in the movie "Spies Like Us".
Spies Like Us:
Milbarge and Fitz-Hume hear a sound Emmett Fitz-Hume: Did you hear that?
Austin Millbarge: Yeah. It's a dickfer.
Emmett Fitz-Hume: What's a dickfer?
Austin Millbarge: To pee with.
Like differential (additional pay for time or duties beyond those normally required, the most common being working a shift other than the day shift), but instead of being paid extra for working odd hours, you're paid extra for your willingness to work with terrible people.
"I got a job as a mall security guard. It sucks, but the pay is decent. I get dickferential for putting up with mall rats."