Note that this is a role playing answer not a system answer
Other The Edge has a mechanism for adding a "sign" to each skill a character has. For example, for a skill called Athletics, the sign could be "wears tight shirt" or "drink protein shakes" or "muscular body" or "wears sports wear". Those give you little indicators of the way a character looks or behaves. You could do the same for your game. Your villain could be rude to the lower classes, he could sport a skull motif in his cloths (cuffs, tie, whatnot), or he could have a tendency to ignore what people tell him (hubris++). This sign does not necessary have to be physical. For a learned skill, you could have "speak in long worlds", "uses Latin in sentences", "quotes others". This gives you a hint as to what their skill/arcana/flaw/merit is.
Catch phrases are good as well as mannerisms or accents (if you can do them, I cannot). Props can do wonders. For that character wearing a gas mask, speak into an empty pint glass when he says something. For that character with a speech impediment, put a few d10 in your mouth. Never us contractions or rude words. Always pause at the start of the sentence and leave the end as if you were still thinking of something new and horrible that you can do. These are other ways in which to convey what the skill/arcana/flaw/merit is although they are more to do with making the character memorable.
Actors are a great source of those. Forget 99% of most villain from Hollywood. Concentrate on the good ones. The ones that makes you think "I love this guy, when I grow up I want to be him". Pick James Spader as Alan Shore (Boston Legal), or Paul Giamatti in Shoot 'em Up, or Hamlet. Look to books and novels. Who makes the best villains? Pick them all. This hints are how to reverse engineer what skills/arcana/flaws/merits a character has from the way they act. Thus, if you take it in reverse you should see what aspect you can use to convey a particular feel.
Now that you have a good villain in mind, think: What skills/arcana/gizmo/advantage best model this fictional and real villain? Work in reverse and you should find something suitable.
Quote from comment: How can I make a catch phrase or a speech impediment communicate that a villain is not only megalomaniac, but fatally so?
Litter the speech with "I", "Me", "how great I am", "I came up with ...", "I am so good that...", "Clearly you would not understand what I did", "You are foolish". Basically, arrogance, hubris, aggressive speak, and putting others down all the time. Add a evil cackling laugh to top it off. Describe the cloths the villain wears as exorbitant, overly rich, and over the top. If anyone interrupts him, make the villain blow up in rage. Shout your players down, stand up and tower over them -- even if you have to get on a chair to do so. It should convey that the character is a megalomaniac fairly well.