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Question for Flapp: Police may not have the right to search your trunk, even if you tell them you have an unloaded weapon in the trunk. BUT, what about weapons that are out in the open? A cop gets a tip that the thief who robbed J Hara is hawking stolen rifles at a public range. A range safety officer calls for a cease fire on the KHSC rifle range. With a dozen rifles on the tables with actions exposed and numerous S/N's visible (in plain sight) to the cop, what is to prevent him from photographing the rifles and running the serial numbers through HPD's back office computer?
I suspect you'd see a whole lot of shooters being yelled at for crossing the yellow line as they return their firearms to their cases.

And if the shooters can't cross the yellow line, why would Cops be allowed unless the range is assisting in their illegal search? Seems like the Cops being across the line destroys the safety justification for everyone else to remain behind the like.

Having a gun in public view doesn't cancel your rights against unreasonable searches. Inspecting rifles and photographing them goes beyond the plain view exception. And the range doesn't have the authority to grant permission for a plain view search of your personal property.
There are 3 conditions to the plain view doctrine outlined in the 1990 US Supreme Court case
Horton v. California:
1. The officer did not violate the Fourth Amendment in arriving at the place from which the object could be plainly viewed.
2. The object‘s incriminating character must be immediately apparent.
3. The officer must have a lawful right of access to the object itself.
The scenario you created would violate #2, as there is no reasonable suspicion based on sight alone that the rifles in question were all part of the robbery. Now, if they saw a rifle fitting the description of one stolen, and it's distinct and recognizable based on some unique characteristics, then the police can make the call that this rifle among all the others at the range is very likely the one (or one of the ones) they are looking for. But, if the rifle is a generic, off-the-shelf, commonly purchased model, then there would have to be more before the cops would have the right to inspect and take pictures of every single rifle being used that day.
The search may also be challenged if the incriminating nature of the item seized was
not immediately apparent (i.e. the officer felt a hard item in your pocket but knew that
it was not a weapon and did not otherwise know of its incriminating nature). It is also
worth noting that for an object‘s “incriminating character” to be “immediately apparent,”
an officer is not allowed to move the object in order to further inspect the item
(i.e. turning the item over record its serial number which shows that it is stolen).
https://www.collinsattorneys.com/plain-view-exception-to-4th-am/To be immediately apparent, the Cops need to first know what serial numbers they are looking for. If they don't find any on the list, they aren't permitted to run the serials they collected through a database search for unregistered firearms. That would violate the "immediately apparent" criteria.
Now, nothing says the Cops can't walk up to each person and request permission to inspect the rifle and photograph the serial number. It's up to you to permit it or deny it.
IMO, if they can't see the serial number from a reasonable distance of a few feet, then they are conducting a search (call it an inspection if you want, but it's a search). Without a warrant or probable cause to suspect that your specific gun is part of a crime, they can't legally do more than ask to see it.
Trying to gather information from all rifles on the benches demonstrates a lack of probable cause that any of the guns they see were part of any crime. They are casting a wide net in hopes of catching one fish without anything to cause suspicion other than a "tip". Did that tip include the specs on the rifles? Description and vehicle tag number of the suspect? Bench location if they were shooting? Without enough of a description, the Cops can only do so much.
And, if they do find you have an unregistered firearm through some mass inspection that was involuntary, the circumstances for them finding out would probably be easy to contest. That would have the case dismissed, but you'd have to register to get the firearm back.
I'm not a lawyer, but that's what I get from my reading on plain view doctrine and the 4th Amendment. Nowhere in the 4th does it say your rights only exist in private places. Even in public, you have the right to not have the police gather information on you and your property that they can't gather without close inspection.
Imagine someone reporting a camera stolen with a vague description. Can the Cops stop everyone in Waikiki carrying a camera in plain view to check the serial number? I don't think so. What about VIN information on your dash? That info can provide some pretty important private information. Can Cops walk through a public parking lot and photograph VINs? I don't think a number you can't read without being inches from the windshield constitutes "plain view."
This old lady called the police to report her neighbor for indecent exposure. She said he was walking around nude in his bedroom with the curtains open. When the officer came, he asked her where she was when she saw the neighbor nude. She took him to her laundry room. He looked out the window, and could only see plants between the houses.
"Ma'am. I can't see anyone next door, not through all the landscaping."
She replied, "Oh, you have to stand on the washer and use the binoculars on the window sill."
