Actually I also read from this very forum that most singaporean
doesn't know this, and asked around. Seems like only the more
experience driver will know, I didn't know it also. Maybe if you
doesn't learn in the books, or if it isn't against te law, no-one
will know. I also don't know if this is a norm in Singapore or not,
but isn't it better to know?
And usually the driver behind would have already been in the same
right lane as you for some time. If you are driving attentively,
you would have notice when he "on" the signal light.