Mine is from my first 'official' email address, that was connected to a studio I started: COPS (which was an abbreviation for Concept Ontwerp Productie Studio: Concept Design Production Studio). 'Hoofdcommissaris' is the dutch world for 'chief of police'. I use that username almost everywhere now. Or my email, if that is what They want. Because most people prefer short names, my username tends to become 'Hoof' a lot of the time. So that is my second nick.