Which part of the phrase “bill them later” was unclear to you?
Bill them for what? If you notice that a property has grown up with weeds and brush and is creating a fire hazard as well as a breeding ground for dangerous animals that threaten the children who play right next to the property, so you take it upon yourself, even though you have no contractual relationship with the property owner, to perform a very expensive cleanup and renovation of the property, when you send your bill to the property owner he will probably laugh in your face (even if he does thank you for cleaning up his lot).