A couple of years ago I testified in court about a 14H motor grader that had been stolen. Apparently the insurance agent hadn't bothered to get a serial number from the owner for a spread going out on a job. The job was in a remote location and all the equipment was parked over the weekend. Come Monday morning the grader was gone. The case was complicated by a lot of things but the upshot was that since there was no serial number on the contract and the owner never bothered to take a picture of the machine, the insurance company denied the claim. The insurance company turned the case over to their SIS, special investigative service, who then commenced to slander and character assassinate the owner and all of his employees. At any rate it was over two years, tons of legal wrangling, expert witnesses, attorneys, depositions and finally a week in court and the owner won his case.
The moral to this story is that insurance is not insurance if you can't positively prove that the machine you own actually exists. Serial numbers, photographs and maybe a third party inventory might be the best insurance you can have.