BBC Programme pages with embedded iPlayer change the title of the page to contain a ▶ (play symbol) when the content is playing.

E.g. http://www.bbc.co.uk/programmes/b01qrn4y

Perhaps this is common but I hadn't seen it until recently.

EDIT: wanted to add that this means you can see that the page is 'playing', but it doesn't work if you pin the tab in Chrome.