That sounds like a good system.
Round here (though Ian_Giles and Squeaky would know better than me) the traffic wardens and Blunkett's Bobbies (PCSOs) seem to leave you alone if they know you're working.
One PCSO told me to leave a note in my windscreen saying as such, so I guess we've got the same but unofficial policy round here (Chepstow, South East Wales (though it's more English than Taffy).