What buff is this orange symbol icon?
Solution 1:
The orange lady above the character's head signals that a flask with the suffix "of Warding" is currently active, which makes your character immune to curses during the effect, see wikia entry.
The symbol for this buff is the purple picture showing the figure with the X above it's head, as seen in the other answer.
Solution 2:
That's not a buff but the Silence curse, which makes your character unable to cast spells.
An higher quality image to show how it looks like on your character:
