The law doesn't say anything about mentioning candidates or parties. Just that you have to say who paid for the ad.
Really, I don't see why that requirement shouldn't apply to all ads, political or not.
Of course all it means in practice is that the sneakier politicians, i.e. most of them, set up more-or-less-arms-length shell companies whose purpose is to pay for ads on their behalf, with names like "Americans for Motherhood & Apple Pie" - but even that gives you somewhere to start looking.