To be fair though, many people who knock on doors are often under instructions to ignore signs saying "No cold callers", etc.
When I've lead teams (in Didcot) of people knocking on doors between 6pm and 9pm (just as people are preparing or eating their evening meals, watching Corrie or putting the kids to bed) in order to carry out travel surveys, I've always made it extremely clear to them that they should ignore any such signs (because our client wanted the maximum response to the survey).
The word "off" seemed to feature quite a lot in residents' responses ;-)