Who's the idiot with the BMW? - Rebecca
That'll be me then.

Dealer has pointed out that the 'sticker' (see thread below if you don't know what I'm talking about) is in fact the edge of the reflective coating. They cut around the rear view mirror so it attaches to the glass, not the coating, and then for aesthetic purposes cut it much bigger than it needs to be. Thought it was stuck on well....and clear...so clear there was nothing there......

Mystery solved. Very embarrassed.

Apologies to those who racked brains for me last week and to those who thought this thread would be more interesting than it turned out to be!