In addition to shooting pictures of parked cars, I've accumulated a small selection of shots I managed to get while on the road. Some of them get partly cut off (though I may use them anyway), while others show the whole car but only from one angle or side.
I thought that may have been an M5 badge on the trunk, which would have been a very rare sighting—according to Wikipedia, only 2191 were produced, and that number includes versions for Europe as well as the right-hand-drive UK version. I don't know how many of them were sent to the US, but I'd bet it's probably no more than 25% of them, since it wasn't a very well-known car yet. But all M5s had blacked-out trim around the windows and tail lights and were only available in black, plus the M5 badge had angled blue and red stripes to the left of the letter M.
Even so, spotting a "regular" 5-Series of this vintage is unusual. I've never been as excited by BMW's cars as many other people are, but I have always liked this generation of the 5-Series a lot. It's probably because back when this car was new, a BMW was still a car for serious drivers rather than the signifier of status that they have become.