I took this photo:

http://www.flickr.com/photos/25124954@N00/480556440/
#comment72157600218892777

Can you guess...

(a) where it is
(b) what it's for?

I know the answer to (a), of course, but would love to know the answer to
(b) as it confuses the hell out of me whenever I see it.

As you can see, other people I asked have no idea. So I thought I'd ask on
UTL ;-)