That's a good tip from Flutterby, but with an "asterisk" added to it...
A PWC is a serialized item with a hull ID number and CF's (assuming it was registered). It's not like finding a football hemlet on the side of the road, the PWC is traceable. He can't just bee-bop on down to the DMV and register it...
Did your friend file a report with the SO or did he just call anonymously about a "theoretical" situation?
By law, anything (and especially an item that is found with a serial number) has to have a "found property" report filed. After a certain amount of time, if the item is not claimed, it can be returned to the person that reported it found. On the other hand, if the losing party then reports the item lost (or stolen), the serial number connects the two reports and the item is returned to the original owner and the reporting party becomes a good samaritan and hopefully gets a reward.
But in the case of a PWC (or any type of vehicle with a VIN/HIN), the local SO (or PD) HAS to file a CHP-180 form and a basic investigation has to occur. Even if the PWC was stripped of its CF numbers, the HID # will be run to determine who the owner is (or who was the last owner). The officer must attempt to contact the last R/O and determine what the status of the item is.
Usually, after about 7 years, inactive VIN/HID numbers are purged from the DMV database and show "no record found" when their ID numbers are run. The investigating officer then has to contact DMV in writing to request a history check of the VIN/HID. It's all part of the investigation...
If the CF #'s were removed and the HID # was ground off, it then automatically becomes a possible stolen vehicle/PWC investigation and further investigation must occur (there is a hidden VIN/HID # on most items). ALL boats have one. Do you know where yours is???
Since your friend has already put some work into it, hopefully (for his sake), the owner doesn't pop up to claim it. Your friend might be out all of his hard work and money!
Good luck!