Legal Sea Foods' "Fresh Fish" campaign is probably too simplistic and sophomoric to be considered truly iconic. And yet ... the ads have proven consistently memorable, and new iterations slated to run on the sides of Boston subway cars will surely grab attention. (And maybe even stir up some controversy, if the city's reaction to certain past marketing blitzes is any indication.) "This trolley gets around more than your sister," reads one of the cartoon-balloon Legal ads." Another ad reads: "This conductor has a face like a halibut." Still another: "Hey lady, I've seen smaller noses on a swordfish." Well, they said the fish was fresh.