my first post

i am on the look out for a 318iS as my new daily drive and hopefully track toy. I am hopefully going to look at one this weekend and have a couple question. Having never looked at one i am wondering what the chances of it being a tarded up 318i are? i have done my reading and think i know the difference but cant actually find any pictures of a m40b18 to compare to a m42b18 engine.
what is going to give the car away as a 318i? i was actually just going to look at vin to see if it reads af93.
thanks
daniel