On my iPhone, anytime music is playing a play symbol appears (and disappears when no music is playing).
How can I achieve a similar effect in the menu bar of OSX Mountain Lion?
Here is sample code for doing this in Cocoa (you can paste it in a new XCode project and build it) :
The only flaw i could see in this sample is i'm using a character for the play icon and not a image. It could be a problem when the encoding messes something up.
You could look at some of the menu bar apps that control iTunes for you. Some of those may have a nice interface for that. Here are a few http://mac.appstorm.net/roundups/music-roundups/five-slick-menu-bar-apps-for-controlling-itunes/