There's a limit of how far the pine tar can go up the bat (18 inches comes to mind). Famous incident years ago with George Brett where he got kicked out for having pine tar well beyond that point on his bat.

For the most part though, the rule is ignored. Definitely not illegal on the helmets, but you'd think they'd clean them up after the games. Probably years of build up on most of those BoSox batting helmets.