I checked out USMB on my Fire tablet and saw it, also. I assumed all mobile devices had it, as I only log in from tower computer on my desk.
The problem seems to be confined to phones, never see it from my desktop at all.
Both of you are correct. Because he is zoomed in so far, this ad is probably from his phone carrier and does not overlay the USMB page formatting very well.
Grampa Murked U -- connect thru your home Wifi and see if it's still there. And get "computer glasses".. There is such a thing. That way you'll have more than 300 characters on your phone screen at the same time.. LOL....