8-11 electric socket changes?

I was watching a movie on Hulu, and I saw a commercial.
Simple green background with a standard Type B (American) electric socket.
And then the little grounding prong, the part that looks like a D, expanded, and became more of a parenthesis. And then the numbers “23” and “8 – 11” show up.
Like so

Anyone have any clue what this means?
I tried googling it but the only relevant results ended up leading me to spyware sites :|