That's how I figured which was which (I don't have the ability to quickly figure out left from right like most people have, so that left me time to play at guessing).
I don't have the ability to quickly figure out left from right
As a kid I used to use which wrist my watch was on as a reference (I couldn't tell right from left, but I did know which wrist to put it on, most of the time). Of course with smartphones being a thing I no longer use a watch, but at this point the brain seems to have learnt to do it automatically. A ring, or wristband, or something like that would also work, probably.
But even then... do they mean my right, or the screen's right..? Or the picture's..? I never know, and a watch won't help with that...