the DC bicycle registration is a joke, WABA (I believe) went to a number of different police stations and found that many of them did not have the stickers and would ask the cyclists to come back later or go to another station; and also that many did not even know about the law. also they often put it on the bottom bracket shell or bottom of the down tube, and many DC cops used lack of a visable bicycle registration as a pretext to harass cyclists of color. since theyre usually on the bottom of the bicycle which isnt visible DC cops now have to stop you for something else if they want to check registration.

for dealing with police: http://www.aclu.org//police/gen/14528res20040730.html