Either a filtering option, or a system where blacklisting a character includes their whole account would go a long way to solving the issue. It's just that I see a lot of people raising a fuss over the filtering suggestion, citing the "community" or new players trying to ask for help as their reasoning. But if players are using /busy perpetually or filtering tells out and silencing them (effectively turning /tells off altogether), then we're already at that point. The original intent for the /tell system has already been "ruined"/"destroyed", so a filtering system would only improve the /tell issue.
Just imagine hearing that /tell chime, and knowing for certain it's a friend/fellow LS/fellow FCmember, that should be a given, not a daydream.