I'd be surprised if there was anything special about the ceramic of a plug making the breaking of glass quiet. A small heavy object, like a sparkplug, on a piece of string, would make a suitable tool to shatter the door glass or quarter glass of a car, and it would be a considerable weapon, too.

The side glass on a car is usually toughened glass, sometimes called tempered glass, which shatters into tiny pieces, and relatively quietly, too. It just goes 'POP' and turns into crystals. Not a breaking glass noise at all.

Windscreens/windshields are laminated glass. A different matter entirely.