UK; they use different coloured tags for international bags not yet cleared customs on domestic flights. In the UK you clear immigration at point of entry but bags are cleared at the final UK destination airport. For example if flying SYD-LHR-MAN you would clear customs at MAN even though flying domestic flight LHR-MAN and most of the other pax on that plane are not clearing customs! The way it works is customs will select some bags to inspect prior to delivery on the carousel, also there are mirrors all along the baggage area so presumably pax are under observation and profiled. It seems like an honour system, but I suspect it is well managed and seems to work flawlessly.