The instructions for the Publisher ID box on the mobile ads widget are
Examples: a14948dbe57548e (for AdMob) or pub-2709587966093607 (for Google)
But mobile Google Adsense ads worked for me only when I prefixed my publisher ID with "ca-", i.e. like "ca-pub-2709587966093607", as in the code for my Adsense ads in my desktop site. The instructions may need to be modified.
I note that the mobile ads don't appear when I go to the mobile site on my laptop, but only when I view from a real mobile. The problem with that is that I have no way of checking the source code served and so what the mobile ad code looks like. I just know that it seems to have ignored my blocked sites preferences, but this could be a temporary glitch.