I have a similar notice on my front door. A Sky TV salesman once decided to ignore it. The conversation went roughly like this:

Salesman: Good evening. I'm from Sky TV. If I could just have a few moments of your time...

Me: I'm so, so sorry.

Salesman: Er...

Me: No, I'm genuinely sorry. It must be incredibly difficult for you.

Salesman: Um... What do you mean?

Me: It must be so tough being illiterate and incapable of reading the sign on my door.

(Slams door.)