The OP incident reminds me of what almost happened to me in a roundabout while driving home on Morse on 1/31.
In the pic below, I am the blue car in the left lane on Morse entering the roundabout. The black car that I drew is the person who entered the roundabout. I am totally legal to stay in that lane and make the exit to continue on Morse, as this original pic indicates a correct move by the blue car.
That black car entering needs to yield to me if going into the roundabout, but does not need to yield to me if turning right into Morse and staying on the right. He came pretty close to me as he was entering the roundabout and not turning right. That driver almost hit me.
So to prepare for that not happening in the future I will use my right turn signal when exiting so the other driver sees and doesn't just jump in there too quick. In these situations the other driver is entering to move into a gap when the right roundabout lane is open, but they still need to watch for the driver in the inside roundabout lane.
I realize there's not much signal courtesy out there, but to avoid someone hitting me like in this situation I'm going to save myself the hassle of getting hit and use the signal. A signal is not needed when continuing inside the roundabout.
Foresake the turn signal all you want when no one is around, but I'm not trusting these drivers to anticipate my moves on the road when they are around me. When someone has the right of way in these situations not all other drivers may know that.
For those who say why not have stop signs instead, roundabouts are considered safer than traditional intersections because they have fewer points of conflict.
How to use a Roundabout