I don't recall ever seeing signs like that in any roundabout I have traversed.
The first time I encountered roundabouts was when I had to drive in New Jersey. I drove for miles, in the left lane, trying to make a U turn. Every intersection had a no U turn sign. I happened to look left and saw a roundabout with a small sign with an arrow that looped around. At the time I remember thinking "only in New Jersey do you have to turn right to turn left".
Apache