> Some places are better than others for placing QR codes. Bearing in mind it takes a while to scan, rather than putting a code in that busy passage way why not put in on the subway train where everybody is rather bored and is playing with their phones anyways.
Because there is no reception underground. (Yes, this is changing, depending on the city. e.g. in London there is now free wifi at some stations, but not between stations.)
Also, some people, when a stranger takes a photo of the ad above their head, will mistakenly believe the stranger is taking a photo of them, and treat it as threatening behaviour.
There is a typo in your <title>: "aobut" should be "about".