This is a genuine BMW push-button, part number 52 20 8 099 548. The number stamped on the part is 52208099548; BMW's catalog files it under the short number 8099548. You will find it on our Interior Body shelf, under Seatbelts.
It fits the E46 sedan and coupe (320i, 323i, 325i, 328i, 330i and M3, 1999–2006), with the M52, M54, M56 or S54 engines — and the European-market versions.
BMW draws it on 3 diagrams, among them Seat, rear, seat frame, through-loading (52_2344) and Seat, rear, seat frame, through-loading (52_2504). It weighs about 1 g (under 0.1 lb).
We have not had one on the shelf yet. Request it and we will tell you when one comes off a car.