Well we are not talking about what a builder does with a chalking gun around your bathroom sink. It is a way of seeding the mind of someone to start thinking about their eternal future without direct confrontation. You can put thought provoking phrases or questions around public spaces in chalk. We use chalk (or non-toxic crayon on the footpath if you want it to be more weather proof) so that it will not damage public property and if someone takes great offence to it they can wash it off. You can also mix it up in the same area so that people are not exposed to the same sign every day.