You should take a look around the UK, they have that sign everywhere, on the bus, at the hospital, and so on. After having lived there for some time and seeing how backwards the country is, I can understand why some people would get violent.
They love a piece of paper, and nothing gives the staff more joy than refusing someone service because their anal rule requires some specific bullshit.
While in the UK in early 2000, I had a bad tooth ache so I called to make an appointment to get it fixed, only to find out that despite paying about 60 bucks a week from my wages for medical coverage, that they will not give you an appointment unless you have a phone number where they can contact you. I did not have a phone or mobile, so I basically got told to go screw by some incompetent cow in a call center, who would not want to slap the bitch in that situation.
Then there was the other time recently, a few months ago I was in the UK again, I had to register with a doctor just in case. I was renting a room in a shared house, and had a contract that showed I was living there and paying rent. However, the receptionist at the clinic would not accept that as proof of address, instead she wanted a utility bill, a thing that I had no way of providing.
So, even though I had paid 1000’s in to the system, it seems I cant get a tooth ache fixed or register with a doctor, because I did not want to give my custom to a mobile phone company or pay 1000’s a month for my own place in central London. Rich and own a mobile? right this way Sr, paid 1000’s in to the system but can only afford a room at the moment? go screw. ... Yea, I can understand why they have that sign.