One thing the “signs and laws can stop bullets” crowd will beed to contend with is that within a few years, the 3D printing and home CNC tools needed to make “ghost guns” will be less expensive to purchase than legal firearms in the most restrictive states. In California, it might already be cheaper to own the means of operating a “ghost gun factory” than to legally purchase a single Glock pistol, and when the government cracked down an banned the sale if the “80% lowers", some of the companies started sharing the plans to 3D print one for free (even Congressional Dems have yet to make a case for how the commerce clause would apply when there's no transaction). When home CNC tooling gets to be affordable, anyone anywhere with the right program will be able to manufacture the reciever for an AR-15 from a blank rectangular block of aluminum (possibly even from one they cast at home using hundreds/thousands of empy soda cans and a furnace made from terra cotta pots and a leaf blower).