A button. Note the dot-dot-dot-dash--"v" in Morse Code. The site doesn't point out an additional factoid: BBC broadcasts to occupied Europe began with the first four notes of Beethoven's Fifth. Get it? Dot-dot-dot-daaaash. Cool.
Update: In order to "balance" my unhostile mention of the BBC, here's a link to B-BBC, currently discussing the false Iraq massacre story the new and not-improved BBC embarrassed themselves with this week.