As I posted in the other thread (but here so you see it)
Arcane Mastery shows in YOUR buff bar (just down and slightly to the right of your character portrait in the top left of screen) - not the enemy's. Arcane Mastery stacks disappear when you aren't in combat. If you look at the Arcane Mastery tool tip at the top of your powers page, the icon used there is the same icon you are looking for in the buff bar. As the buff bar goes alphabetically, it's usually near the beginning.
Chill stacks show in the Enemy's buff bar. - Looks like a snowflake icon.
Comments
Arcane Mastery shows in YOUR buff bar (just down and slightly to the right of your character portrait in the top left of screen) - not the enemy's. Arcane Mastery stacks disappear when you aren't in combat. If you look at the Arcane Mastery tool tip at the top of your powers page, the icon used there is the same icon you are looking for in the buff bar. As the buff bar goes alphabetically, it's usually near the beginning.
Chill stacks show in the Enemy's buff bar. - Looks like a snowflake icon.