A really nice idea (I already knew from other cities) is a block of notes to be left as just a friendly reminder to motorists illegally parking their vehicles in bike lanes.
Do Not Park In Our Lanes!
Your vehicle is parked on a bike lane and/or footway! This is an offense against the road traffic regulations and can cause an administrative penalty up to € 726 and a towing with cost. In case of repeated disorderly parking you can reckon with a complaint.
I had this dialog with the nice lady in the town hall who was giving away the blocks.
Lady: How many would you like to have?
Me: Two or three, please.
The lady began to tear three sheets from a block.
Me: No, I mean three blocks?
Lady: But this' very much!
Then she gave me one block á 20 sheets.
Me: Thank you so much! This will do for a week!