[Aezeal]

another option (I'm not into that ascii thing I think you said he's using) might be different color backgrounds behind the symbol. that color would be most obvious and thus could represent the most obvious thing about a unit.. I'm not sure what would be most obvious though.. race or general weaponry (heavy cavalry/infantry will probably first be noted for being just that... though huge giants will probably be seen for it's race first..
as would undead.. unless they where in heavy armor since you'd not see the bones untill you smashed the armor..

in your first example you used G for guards.. OFTEN the class of a unit is clear through its armor so I'd not use both.. if a wizard is wearing heavy armor he'd probably surprise you by casting spells "IRL" too.

So I'd use a block of color for general appearance. grey = soldier, purple and red = wizard, yellow = noble, brown = peasant etc with differences in that color indicating it's relative power (light grey = light infantry, dark gray = heavy infantry, light brown peasant in regular clothes, dark brown a person in leather armor) the symbol could then indicate race or something, and the color of the letter something else ..

If you could draw a thin line around a box or just a stripe on it's 2 sides that could indicate casting of a spell..

hmm brainstorming is nice but it'd be better to see what the creator is acutally doing.. all these thoughts are probably wasted since he has a plan anyway and I can't program this for myself