"Strictly"

I've mentioned before that every office building here has a small security checkpoint on the way in. Metal detector, a guard or two, x-ray belt thingy for bags, etc. Nothing more than a moment's inconvenience.

I noticed also today that there are usually signs up indicating that only people who have business to be there are allowed entry. Makes sense, of course. You don't want random people off the street walking around your office building. We do the same thing in the US. But today I finally noticed what the sign that indicates this at my office actually says:

"Strictly" No Passersby

Why is "strictly" in quotes? Is there a joke I'm not getting? Or are they just not very strict about it?