Here's a link to the Massachusetts Dept of Transportation's guide on designing/building roundabouts:

https://www.mass.gov/doc/massdot-guidelines-for-the-planning...

It provides solid guidance on how roundabouts should approach crossings to minimize risk of accidents or collisions without impeding traffic.

Probably the best graphic is on page 45, figure 5-13

Some do have stop signs before you enter, but they should always have at least an implicit yield. Vehicles entering should be prepared to stop in case there's not room to enter the roundabout yet. The real issue with their suggestion is that only being able to cross "before the entry" wouldn't get you anywhere, you have to also cross where cars exit it!

Normally they are for pedestrian crossings. The stop for the incoming traffic will be near where the vehicles yield prior to entering the roundabout but the stop for outgoing traffic is several cars away to allow cars to continue moving in the roundabout.

And because they are pedestrian crossings, they only go red when someone is walking across them and for a few seconds before and after. Which means in most cases they are green 90-95% of the time and only go red for less than a minute at a time.