I had a rattly old Triumph Spitfire in my younger days. It used to vibrate like mad at 60mph. The girlfriend at the time said I ought to get a personalised number plate for it and suggested:
D1 (the moderator may want to cut this) LDO.
...though I do agree with an earlier post about how "uncool" they are. I find it rather sad myself, but I have to be careful, the brother-in-law has one.