I have Mavericks running on my Mac Pro and I have no interest (at this time) to upgrade to El Capitan. Recently the El Capitan upgrade notice as appeared on my desktop and will not allow me to dismiss it. It's annoying and it is covering my primary Mac hard drive icon. I've gone into the App Store and hidden the El Capitan upgrade notice from there. However the desktop notice remains. Is there a way to remove this notice?