Accentuate the Positive!
This is kind of a music nerd joke - the accent mark over a 'plus' sign to indicate that the viewer should "Accentuate the Positive". It's executed in a Jazz font that most musicians should recognize from printed sheet music.
It's a simple iconographic representation that will resonate 'positively' among those who "get it".
From a production standpoint, it can be executed in white against any dark background or in black on a lighter background. Other color combinations are clearly possible: pink on blue; yellow on orange.