its simple, right lane is for 90 degree turn or 180 only
left lane is for 180 and 270 only
you always signal if you change lanes but there is NEVER a reason to change lanes in a roundabout and doing so is usually crossing a solid line.
you MUST ALWAYS signal when you leave a roundabout so the only time you signal entering is when you are in the right lane and will only be going 90 degrees and exiting.
I always find it interesting that when I move into the left lane some people find it necessary to suddenly speed up just because I want to enter the circle in the proper lane, it's probably the same ones who go 20 in a 30,
but when you go to pass, speed up to 40, sheesh!