on modern BMW's:
i = sedan
Ci = coupe
x = 4 wheel drive
The number used to indicate model and engine size: 330Ci is a 3 series, 3 liter coupe, a 325i is a 3 series, 2.5 liter sedan. You have a four wheel drive 3 series with 2.5 liter engine. 5 and 7 series don't come in Ci. A 540i is a 5 series sedan with a 4.4 liter engine . X5's & X3's are all 4 wheel drive.
Some rare cars, like the 8 series 850Csi get a special "csi" tag. It's the highest performance non-M rating. It's also a nod to it's predecessor the 6 series and the 635csi. It's confusing because the M6 of that era was technically the called M635csi. Though M6's only had M6 model designation emblems and there was a 635Csi that was a step below the M6. There was also a 633Csi, 635Ci, 633Ci, etc...
There are also BMW internal chassis designations. For the 3 series, it's E30, E36, E46 and the new 3 series, E90 sedan & E92 coupe. This is never listed as an emblem.
Then there is the problem of people putting M emblems on non-M cars. Why they do this is a mystery to me. Only people that know the difference will notice and what we'll notice is that you're a poser.
Those are the basics. Good luck in your search.