I've no idea, and their website seems deliberately vague, not even mentioning the country/countries in which the chess match takes place. The cast list, however, doesn't list any of the extraneous roles from the Brodaway book (Gregor, Young Florence, Nikolai, etc) ... but it doesn't list Svetlana either, so who knows.
The cast list is here: http://www.theatermania.com/washington- ... 28089.html
It's a small, tight cast at 14 (15 if Svetlana isn't listed) - which would lend itself to something more London-like without all the small speaking roles. If I had to guess, I'd guess they're doing a blend of some sort, leaning in the direction of London... it'll be interesting to see what Sam French lets them get away with. **takes notes**
EDIT: I just noticed, the Signature Theatre website does give Richard Nelson the book credit, so it looks like they're doing a streamlined variation of the US version, much like I'll be directing this fall/winter, so it'll make for good study material!