On the motorbike, I think it was called 'showing'. And, yes, I do it on my bike - though not exaggerated weaving about. Basically, it's just moving out of the single line and across the SMIDSY candidate's field of vision.
For example, and I'm not sure of the science here, I believe if you approach a junction in a straight line, as a cyclist might, that it is possible for someone sat at that junction to not see you. They might be looking your direction but your presence simply does not register. It's not them being inattentive, or whatever. Their eyes physically see you but quite literally their brain filters you out. Dunno why. But by breaking away from that line, say moving secondary to primary, your crossing their field of vision and their brain clocks you. That's why eye contact is important. It lets you know that you've been clocked. Still no guarantee that they won't pull out though! But moving to primary also gives you more time to react if they do pull out, so it's a doubley wise thing to do.