In England, as children we might have said 'I call dibs on that' or for short just 'dibs!' I have no idea what 'dibs' might mean outside that expression!

Hey, Robert! You're right, it means "the front seat is mine" It's pretty much something only a child/teenager might say, imagining the front seat has some prestige attached to it or something, haha.

Two more "intriguing additions" for you, Robert: In Britain, children ( typically siblings) also say 'Bags I the front seat!' or 'Bags I the last chocolate muffin!' for whatever you want to lay claim to. These expressions often vary according to region. At a guess, I grew up in a different region from Karen. There's also the American expression - an extension of the one you heard - calling shotgun. "I call shotgun!" comes from the expression "riding shotgun", dating from the days of the Wild West when stagecoaches had an armed guard next to the driver.

Using "call" is like saying " I declare to everyone that I am taking the front seat." Childhood rules state that making such a declaration is the equivalant of actually possessing the object, however if 2 people call it at almost the same time, they might tussle to decide who should get it.

I call something first means I said it first then I have the right to o use/choose/pick something first. before anyone else.