Using magiboards and blackboards for public demonstrations instead of placards

For those who are politically active and take part in public demonstrations- especially environmentalists, a great way to post public messages in demonstrations is to stop using placards which take up paper resources. Typical usage of placards for public demonstrations pictured below:

Using a placard only allows a message to be written once. But by using a magiboard or blackboard to display a message, you can erase it and use it again and again. This will also reduce paper resource consumption as well as costs.