Comment 2 for bug 800256

Hugh: correct; the blue colouration of the pips/triangles next to the icons in the Launcher indicate which window(s) have requested attention.

Learning the association (same as for the colours used in the interface) is quite likely going to be a subconscious activity were repeated exposure and predictable behaviour lead to the association without needing to be explicitly taught (as you've found). In a way, the blue notifications/pips can be seen as an optimisation stage: little is lost if a user does not immediately notice the hints but they aid the user without resorting the alternative behaviour of flashing something up on top of their desktop.

Of course, details such as the shape and style can continue to be subtly refined based on feedback and testing.