Oh yeah forgot that some of the later cars have a roof mounted aerial. Personally I prefer the "hidden" earial in the rear screen instead of having the lines spoilt by a large protrusion!!!
Next time you de-mist the rear screen you'll notice the top two bars dont clear....thats the aerial! Only bad thing is if you get a break in the heated elements you lose radio reception. Metallised paint will cure it.
Aesthetically I prefer the window antenna too, however as a broadcast engineer, it'll never give as good performance as a decent rod- which is why there is an amplifier behind the trim.
To be strictly accurate, the top two strips are the medium wave aerial , the FM aerial is combined with the heater elements. If you have a broken strip, you will notice that FM is Ok until you turn on the demister, at which point the radio craps out. As Wrinx says, fixing is easy using conductive paint and masking tape.
I bought my 155 two days ago, and didn't know where the antenna is ! I'm glad to read it's in the rear window, cause I don't want to make a hole in the body... Even if it's not very efficient (in my gtv6 it's in the front window), I'd rather not have a good radio reception than make a hole !!!
Finally I found the antenna wire, but it's not connected to my rear window (155 1.7 TS 1996).
So I bought a little electronic antenna, and glued it at the bottom of the rear window. It's invisible, and works perfectly ! (cost me 15 Euros...)