It's the inevitable reaction of what to do about every single possible problem that might arise from granting people controlversial freedoms. I don't know how much controversy surrounded the idea of permitting brothels, but now there's a controversy over the signs. On one side, people want to feel that the whole thing is being managed somehow so they feel safer. On the other hand, they don't want a bunch of advertising which may stir up undesirable effect.
So, as far as I can tell, the problem seems to be addressed with massive amounts of bureaucracy. I found one PDF that referenced not only safe sex but zoning, parking of cars, discreet appearances, linen (!), storage and handling of contaminated waste (!), and much more.
All of this pushing against the fact that people <i>pretty much do what they want to do anyway</i>.