|I spy a sound icon|
This has been a long wanted feature from many people.
And, as always, Google slowly rolls out new features. So, you may have gotten your already, or will soon be able to see which tab sound is playing in. I found a news article from way back on November 13th, 2013 mentioning this update, where it was in beta.
And, there should be a link to the XKCD comic/article that mentions this feature. That comic was written a long time ago. Hopefully, I can find it again.
~ Danial Goodwin ~