Shortcut for Rolf Ade.
Also the domain name abbreviation for Germany.
I should note, that my Wiki and Tclers Chat shortcut has nothing to do with overeager national pride (or national pride at all), although I'm in fact a German. It may sounds surprising for those, who suffer from my somewhat limited abilities, to express myself in English but I made my livings for a dozen years as writer (during study and years of wandering) for a local daily newspaper. In Germany, it's common to sign most of the articles in a newspaper not with the full name of the author but with a few-letter author token. My first chief editor gave me, as would that be self-evident, the author token 'de' - he simply stripped the first letter of my family name. Since that time, I used this 'de' as author token, nick name etc. at some occasions.