James Mercer’s dad was in the Air Force and he lived in Germany when he was younger. “40 Mark Strasse” was a nickname for a two-lane highway (Bundesstrasse 40) that ran between Kaiserslautern and Landstuhl, both of which had large American military populations. Prostitutes — some young, some not so young — used to streetwalk along the side of the road, and the rumor was that 40 Deutsche marks was enough to get you some action. This song, I take it, is his plea to one of those girls to give up what she was doing and get her life back on track.