AbdulAlhazred
Legend
A mark still applies the -2 penalty to attack rolls for attacks that don't include the "marker" as a target. Misdirected Mark is essentially a debuff, and used properly it can be an effective tactic even without an ability that triggers on an attack by a marked enemy.
I don't know what -2 penalty it is you are talking about. Show me ANY rule in the game that says that a target marked by a rogue has any effect put on it at all. Only misdirected mark or some similar power can create such a mark, and there is no rule for what that mark does. The -2 to hit anyone else thing is a part of the fighters class feature, Combat Challenge. A rogue has no such feature, and thus any mark he creates has NO effect. It doesn't give a -2, it doesn't do anything. Unless there is some generic rule for what marks do, which I don't find anyplace in the PHB.
Thus it is worthless for a bard to allocate a mark to a rogue (or a cleric, or a wizard, etc) because they can't DO anything with it. It is only meaningful if the mark is allocated to a fighter or a paladin (and it is a bit murky with paladin because his mark comes from a power). I would have to read swordmage to know about that one, but I don't recall ANY class from PHB2 that lays a mark either.