Not at all. That is the beauty of these plates, they are registered to your car (transferable to any of your cars) in your name so you have full ‘ownership’ rights. If someone stole the plates and put them on their car, the police would know immediately as that car is not registers in your name.
As you own the plates, not the Department of Motor Vehicle, you can sell them on the open market like a share. The limited number of historic plates is what drives the price up as people want low numbers, Number 1, sold for over $10 million recently. Other birth year numbers and unique combinations, or plates with 8’s in them are also highly valued. Supply and demand, and unlike tulip bulbs, they are not making any more original historic plates so the value is what it is. Maybe demand will dry up but they have been rising for the last ten years, so who knows.