The answer is don't turn right, that road is closed. Or to be more accurate, that's how it's being used in the specific case I saw. It's positioned at a traffic light controlled crossroads, and a high wall means you can't actually see the roadworks to the right.
I thought it was a crazy way of signing the closure. Arrows are normally used to direct traffic rather than to point out where not to go. If they want to tell people not to turn right, surely they should use something like a right-turn arrow with a line through it? Or just write "no right turn" on a big sign.
The first time I saw it I thought it was a little confusing, but wasn't sure if it was me being daft. Today I saw a car slam on the brakes in the middle of the junction, as if he couldn't work out what he was supposed to do.