The simple answer is: play with your keys.

The first thing I bought when I got my first real job after graduate school was a new BMW. I can't count the amount of times that I'll be in a bar twirling my keys between my fingers, place my hand (with the keys in it) flat on to the bar as I turn away from a HB, order a drink (or talk to a friend) and be asked by the HB "what type of car do you drive?".

Yeah, as if you didn't see my keys.

She knows what type of car I drive so there's no reason to be specific: "Oh, I treated myself to a brand new convertible this year. Why?"

At no point did I say BMW. At no point did I brag. I merely responded to her question with a vague type of car.