I salute you Robert, I use the indicators also in the same way, if someone is lapping me or even drafting me I use the signal to clearly show that I am aware of the car behinds intentions to pass, my intentions to allow that to happen safely (for both of us) and expect the following car to pass on the oposite side to that I am indicating thus making it much easyer (and faster) for them to pass.
I thin what you do shows respect and awareness
I too have seen the oposite indicator used and I think this is a location thing, in another thread (I will find it) it was stated that some eastern european HGV drivers signal this way to allow you to pass them on 2 way roads!! now if a 40tonne artic indicated right here in the UK on a 2way road, if you overtake expect to get a: half way alongside the trailer as the driver forces you off the road as he overtakes somthing himself (as he was clearly indicating to do) or b: sees you in one of his 10 or so mirrors, and hits the anchors giving a little parp and a nice 2 fingered salute as you pass the unit, whether you see the tractor doing 25mph ahead in time is, anyones guess?.
b: is more likely because IMO most truck drivers are way better than you avarage car driver at least near where I live, and we get loads of international lorrys passing thru here, as I live close to the main port and 99% are superb drivers.
I didnt find the thread, grrr
S(hic!)D