Lacking knowledge on this: Appears the firearm just became "concealed" (possibly without permit?). Also seems suspious to mask a firearm this way when a LEO is present.
This was in response to folks not wanting their gun serial number relinquished. I would think this would set off less red flags than placing tape over serial numbers.
You would have to have a CHP, or no access to a key for the bag. A pocket knife in your pocket, would be access to the bag, so I would not suggest doing this without a CHP, and your second approved photo ID.
I could care less about having Gov know my gun serial number. I fear someone not checked out with my handgun, unloading it. What if he Negligent Discharges my gun, and puts a round in his leg, arm, hand or right between the eyes. His brethren rolling up to that stop, are not going to swarm friendly.
If someone were to try the bank bag idea, Bag the gun before he walks up, tell the puzzled LEO, as you hand him the locked bag, you are concerned with his safety, and you will not allow him to handle your gun unless he wants to meet at the gun range on his day off, and you can check him out on it. This will work best if you show him your NRA Chief Range Safety Officer ID.
I do not want to be the first one to try it, but it would make for an interesting forum thread. I will seek out a LEO friend, Chief Of Police, retired, and ask him what he thinks of the idea.