Wilton St stop in London is a red roundel on a white background and that
always meant a compulsory stop. A request stop was always a white roundel
on a red background. Has that changed? I ask because it seemed to me
that the only way you guarantee a bus to stop was by raising your hand. I
watched one man move to the stop (from his waiting place in the set-back
shelter) as his bus approached and then look surprised as it accelerated
away (it wasn't full). Almost everyone felt the need to raise a hand to
hail the bus.

To be fair, some buses were already indicating to stop before the hand was
raised but I got the definite impression that a compulsory stop wasn't
compulsory.