@Joshi
(In case it isn't obvious, the following applies to Australia, where we drive on the left.)

I've done hundreds of thousands of clicks on country roads, and the right-turn signal has NEVER meant that it is 'safe to pass'. Never.

Most indicator stalks allow drivers to apply pressure and thus activate a turn signal's bulb, without "locking on" the relay.

This allows drivers to manually produce two or three pairs of LEFT flashes of the LEFT indicator. Like, L-L (1 sec pause) L-L (1 sec pause) L-L.

That has always been understood that the driver in front is saying, to the following driver, "I know you're there. I'm not turning off, but if you want to pass, it's clear ahead, and I'll be looking out for you."

The right-turn signal has ALWAYS ONLY meant, "Danger. Do NOT overtake me."

More than a few times, I've been in trucks with several tonnes of explosives and an impatient passenger coach, or cara-bloody-van, starts showing too much of their grill in the right hand mirror.

Giving them the L-L pattern has let them know it is clear to pass, but the right-turn signal coming on has ALWAYS meant, "Nup. No way. Don't be a bloody fool. Cool ya jets."