[esskay]

Signage exists. Plus the vast majority of times painted ones are used in areas where almost everyone on the road knows how it works, and within minutes of it snowing a very clear outline of the path cars have taken would make it abundantly clear what the process is.

Roundabouts are engrained into UK road culture, you'd seldom find a driver in the UK that cant figure out how one works, even if they may not have great lane discipline on the larger ones.