Usually, when you see a reference to a "Euro" car, you're seeing a car that was originally purchased in Europe, and someone paid to have it shipped to the U.S. Either that, or it's someone who's pointing out that it's a "European car", and you go there to find out that the car was actually sold in the U.S. There isn't a "Euro Package" per se.
Now, if the car is a genuine European-market car, there'll be a few tell-tale differences. First, it won't have a 17 digit VIN...the first three digits will be the chassis number i.e. 123 for a '77 to '85 300D or 240D (take a look at
this thread for more info on the chassis numbers). Also, the front bumpers will almost invariably be smaller than on cars sold in the U.S. (the Euro bumpers don't meet DOT specs). Sometimes, a Euro-spec car will have a different headlight arrangement (for instance, square headlights on a W123 instead of the round lights you see on a U.S. model). However, the headlights are not a given, because the U.S. inspectors often required that the headlights be changed to the U.S. spec lights, and there are also many aftermarket "Euro Light" kits out there...so even a U.S. spec car may have "Euro lights".
Really, though, the best way to tell a Euro car is to look at the interior. Most "features" that were considered standard equipment in a U.S. spec car was treated as optional in a European-market car, and as such, many "Euro" cars are more "bare-bones" by our standards. Although it is not unheard of, it is VERY rare to find a true Euro-spec car with power windows, the automatic climate control setup, or an automatic transmission. Just about ANY Mercedes with factory cloth seats is going to be a Euro-spec car.
There are also various models that were only sold in Europe, or were sold in Europe after being discontinued here. The most ready example of this is the 240D. 240D's were no longer sold here after 1983, but they continued to be sold in Europe until the end of the W123 run in 1985. I believe there was also a W123 220D, that never made it to the U.S. market. The non-turbo 300D was also sold in Europe until the end of the W123 run (it was replaced in 1981 with the turbo 300D here), and was typically sold with a 4 speed manual transmission.
A lot more could probably be said on the differences between Euro-spec cars and U.S. spec cars, but I think you get the general idea.
Euro-spec cars are a bit of a needle-in-a-haystack find, although eBay has made sightings a bit more common...
Hope this helps some...good luck!!
