Getting around in one piece

Policemen, firemen, and prison officers travelling around Berlin are allowed to use public transport for free, not just while performing their official duties but also when commuting to and from work.  The only stipulation is that they have to be wearing their uniforms and not civvies.

A good move on the part of the city authorities - this is one section of society that deserves as much help and support as they can get.  (Some may disagree with me here, but that's another story).  The philosophy behind the idea is that the presence of uniformed law enforcers on Berlin's trams and trains would act as a deterrent to would-be vandals and yobbos.  

A good idea in theory, but there's a problem.  The employees in question don't want to travel in uniform.  They prefer to pay 91 Euros (3 zones) for a monthly travel ticket and use public transport incognito.  Why would they voluntarily pay so much when they could travel for free?  

Policemen, firemen, and prison officers say they don't like to use public transport while in uniform because they are molested by other travellers.  Makes you think.