My wife and I like to leave behind clues that we're a couple on the run when leaving budget hotels. Empty hair dye boxes, cut-outs of passport photos, randomly annotated maps. Never get to see e fruits of our work, but I hope it has the desired effect.
@falken @spacemagick @fesshole Sometimes people mark bills in a distinctive way when they're doing something spy-like or detective-like with money. A red X would be more noticeable than a UV-reactive ink or a highlighted corner or a circled serial number or a "GAY MONEY" stamp or a moustache drawn on the face of the person on the note. Obviously, don't do this in countries where defacing the currency is illegal.