Combos are Obvious.  Each one has unique Essence flares associated with the particular Combo.  There's really no way to make them subtle, since you're basically forcing multiple Charms to work at the same time, when you're not normally able to do so.  That's going to result in a fancy light show.  The only time Combos are -not- obvious is when they're used in social combat or dramatic actions.  Combat Combos are -always- Obvious.  And Obvious precludes subtlety.