This is the Metropolitan Police’s Marine Unit. They have jurisdiction of the canals and rivers in London.
The police advise that we familiarise ourselves with the local area each time we moor somewhere new, so they can get to us quickly if a crime does take place.
Look for a street sign or memorable sight and calculate approximately how far you are from, it in which direction.
E.g. “I’m moored on the EAST side/towpath of Regents Canal 50 metres NORTH of the junction with MILE END ROAD.”