OK - You look at sticker which says no door-to-door sales, no jw's, no mormons, no tradesmen etc.
Unless it specifically says "No window-cleaners" you've got a loophole.
Householder: (Door creaks open) You rang?
You:- (Dressed smart/casual, no f*gs) Oh, hello - I'm Drew, the local window cleaner - I clean several of the houses in your (road, area, block) and I'm looking to fill a couple of gaps in my round - I'm sure you'd agree it's difficult finding reliable workmen nowadays - would you like me to quote for your requirements? I can do it right now or whenever's convenient to you..... (shut up and wait for response)
Householder: Ok
or:-
Householder: Naaah! (Or words to that effect)
You: OK, thanks for your time have a good evening, bye now - oh here's my leaflet if you change your mind I'll be about (next week, whenever) look out for my car - it's an (orange estate, Ford model T, etc) just come and ask me.