1. A strong and sickly sweet smell.
  2. Equipment to grow cannabis being taken into a house. For example, lighting and ventilation equipment.
  3. Constantly covered or blocked-off windows. Cannabis factories often have constantly pulled curtains, black-out blinds or foil coverings.
  4. Unsociable coming and going at all hours or neighbours you never see.
  5. Strong and constant lighting day and night.
  6. High levels of heat and condensation. Cannabis factories often give off heat and the windows stay misted up.
  7. Constant buzz of ventilation. Listen out for a whirring sound as the growers try to create an ideal climate for the plants to grow.
  8. Lots of power cables. Gangs dig underground to lay cables that hook up to things like lamp posts so they don’t have to pay for the enormous amounts of electricity they use. They can easily bypass a £20,000 utility bill.

Suggested by seanie567 with Crime Stoppers on twitter as a source.