Aha! My ad-memory was correct. Not that these are easily forgettable:
http://www.eatmedaily.com/2009/08/nyc-subway-ads-human-fat-pouring-out-of-bottles/

Just a note that, unless my subway-ad memory is playing games on me, this is playing on an old riff for the NYC Health Department. For years now there have been on-again, off-again posters of disgusting-looking “fat” in soda glasses on the subway. Besides the question of fatphobia, my gag reflex says there must be [...]