If you've seen small piles of flour and chalk markings in your area, it may have been a Hash group like us.
We've opted for harmless chalk and flour to sparingly mark our route as they are biodegradable and easily wash away.
We do try and inform people we meet as we're setting our runs (all on public footpaths and roads) what we're doing and what the materials are but, if we missed you, at least you now know what the marks are.