"Marking" Opponents

So a lot of my mechanical ideas for my game are based on D&D 4th edition and similarly tactical tabletop RPGs. The way that game implements tanking- in the absence of "aggro" mechanics- is, tank-style classes can mark opponents, which gives them a penalty for attacking a character other than them and usually punishes them in some other way. (For example the Fighter gets a free attack on a marked enemy who tries to attack another PC.) Similarly strikers/DPS guys usually have a mark of their own which gives them an advantage attacking a specific opponent.

So the question is how to make status effects "remember" who inflicted them on you. The cheap way to do this would be, since I've only got 5 characters in the game, make it so they have fixed classes so only "Bob" is inflicting the Mark and therefore the condition is "if you attack anyone other than Bob, X happens" (rendered in programming-ese of course.) But supposing I wanted to make it possible for characters to change classes or swap abilities, a la FFV or whatever? How can I make a skill or status effect say "if you attack anyone other than [the character who inflicted this effect], this happens"?

not 100% cus not good at the more advanced stuff. but maby could have the mark skill apply state to caster at same time. then ur "if attack other then bob" change to "if target has state (nothing happens cus Bob has state) else, X happens"