Unownable doors

Hey guys, I’ve been working on this gamemode of mine and I already have it so you can own / sell / set doors to ownable / unownable. In some other gamemodes, I see that some doors are set automatically to unownable. I was wondering how is this done so when the server starts certain doors are automatically set to unownable using my system. Is it through like a doors ID or something? I’m confused : /