I've heard (perhaps just a rumour), that for "Alpina"-tuned BMW's there was a kind of blind or curtain for the back window available. If annother car was too close in the back, you could lift up this blind, on which was written: "The new Alpina B6 with xxxx ccm and xxx hp wishes a pleasent day and says 'Bye Bye' " - and then you make a kick-down.