The law actually reads that if the key is property of a government agency and stamped that way it is illegal to copy and everyone I know honors that. GV Lockshop has a ”do not duplicate” stamp that we can stamp on your keys but it really has no power. It might stop Home Depot but that is unknown. The best bet is to actually upgrade your keys and locks to a “Patented” key system. This will cost a little more but you can be guaranteed that most people would not even have access to the key blank.
The Locksmiths that might have access to this blank would not risk losing their license to sell this product, by making 1 $10.00 key for someone that did not have the proper authorization. Look for the Factory stamping on a key that says Patented High Security and some kind of factory control number as well. The same way as computers change yearly Patented key systems are constantly evolving.
GVL stays on top and offers current products that are Patented until 2029 as of today.