You're correct Axon does appear to insert the Invisdot data "somewhere" within the the Ancillary data using Operational Practice-47.
I was hoping I could find specifically what data it was carrying and where. It looks like ITV specify it on line 15 but the AXON manual link that you attached implies you can put it on any line you like.
At this stage I'm only interested in knowing which bit or bits change as its turned on or off (although it'd be nice to know if it carries any other flags too). With a Tektronix Scope, an Axon card and on an ITV job I'm sure I could figure it out in a few minutes. Unfortunately I have neither at my disposal.
Looks like it might be carried in Packet 31 of a WST stream?