Closing time at the bar

A man completely drunk is kicked out of a bar at the closing, he staggers to the parking lot and stops in front of the first car, feels the roof for 30 seconds, says "don, this one ba" He struggles hard to the next, feels the roof for 30 seconds and says "don, this one".
He walks towards the third car and there, the bartender who has been watching him for a moment asks him:
- How do you recognise your car just by touching the roof?

The drunkard answers him
- It's easy, my wife, she has a blue beacon on the roof.
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