ok fair enough, lets just say they were told not to approach house or communicate with person concerned. They are not random in the sense they were told the person was not interested at least 4 times. I think maybe it is cos one of their workers is delivering who maybe do not know and apparently cannot read
Or maybe the Politician and his volunteers are pretty busy going door-to-door and haven't noticed the sign. As its rare here for private homes to request its not like the 'no soliciting' signs people in that line may be used to in the US or other Countries and know automatically not to post in flyers.
IMO if your friend actually has grounds for actual and real harassment by this Politician (which flyers in the letterbox are not) it should be dealt with legally, likewise if its something unwinable or if its something simply in his head he needs to learn to let go before it affects him badly.