Savies??? LOL. Nope. Never heard that one.
We would "call" our seats, like on the way to the car. Didn't matter is someone else was twenty feet ahead of you, if you called "shotgun" first, you got it fair 'n square.
Of course then you had to deal with knees coming through the back of the seat, and your hair being pulled, and your ears flicked, or the dreaded twisted up rubber band being stretched and let loose in your hair right at the base of your skull...that's as bad as gum to get out, and as painful.
But sorry, no "savies". If we had to get up from chair or something we would just say, "this is my seat, don't touch it or I kick your butt." That never worked but we always tried.