Chalking

Chalking is communicating to a mass audience by using chalk on concrete.  This typically means that information is placed on the ground in a place where people walk. 

Nothing catches a pedestrian's attention quite like a winding 2 block long short story that trails from a bus-stop all the way to a resturant.  Areas of high pedestrian traffic that are not in an enclosed location are great targets for chalking since rain can get clean the location naturally.  Concert and event notifications that are non-recurring are good candidate ideas for chalking since they are sure to disappear (by magic) before they become too dated.

Since it's not permenant it's not destruction of property!

Doesn't that argument sound reasonable?  If you are interested in spreading a message for a limited period of time chalking may serve you well.  If you are concerned with personal property rights and are wary to do things like graffitii and wheatpaste in order to show your respect of property chalking may also be something you might be interested in.  Using actual sidewalk chalk ensures that a good blast from a garden hose or a light rain will remove the message from the public.  

Chalking is usually resistant enough to the shoes of pedestrians to not become overly smudged too quickly.  Without rain or intentional removal chalked messages can generally last for 3 days up to 10 depending on humidity and other envionmental factors involving water (and magic).  Using things like rock and other materials as chalk can last quite a bit longer but any 'scratched' message will eventually go away.  Unless you use something radioactive maybe. 

Sure it's a huge amount of work for a few days of use but at least it can only be limitedly targeted by geographic location!

Chalking for intentional messaging is only effective in extremely specific instances.  Social events and concerts as well as speeches and city council meetings all work well as things to chalk.  Your market is also only segregatable based entirely on physical locations.  Geographic recon in a region should provide you with a really good idea about your target markets.