Martial power is evidenced by the almost impossible levels of physical prowess they exhibit. It's not a subtle thing for non-subtle powers. Observe Batman and tell me he looks like a regular joe when he's kicking someone's ass.
Primal has buttkiss to do with plants, and everything with spirit inhabitation. Are you saying that a Barbarian who has the Spirit of the Frostwolf inhabit him and cause his weapons to create cold damage doesn't have some sort of show of that power? Do you think that he just gets very angry?
Divine agents often cause their weapons to glow and explode with radiant power or thunder or fire. If they're not shooting pew pew laser beams. They don't need -angels- to do so.
Arcane agents make frikken fireballs appear to blast enemies to bits. They're not exactly -subtle-.
A psionic agent who uses his mind to throw a foe off a cliff before battering them with telekenetic force bolts on their way down doesn't get to stand there looking innocent with no evidence that they did it. They don't have special 'I don't appear to be using my powers like every other character in the game' rules. And so, halos.