Yeah, not sure who was the 'genius' that allowed this, but you can have ads on the lockscreen now. Many apps have implemented this, unfortunately, and you'd have to check which one is causing it. ES File Manager was one that notably got backlash for it. Not sure, but maybe an Ad Network detector app might be able to pin point which apps are pushing ads, and that way you might be able to see which app you have to check. Most allow this to be disabled in their settings, however, so you don't have to use that charging screen, but they enable it by default, obviously.