I don't remember the colour, but IIRC, quest items are exclamation points.

This is something else. Those yellow exclamation points hover over the head of an NPC.

Now that I've had a better look, it's shaped like an eyeball with a vertical slit (like a lizard eye?) and sits to the right of the onscreen character and pet heads. NOT the little HUD icons beneath the protrait, but next to the character in the gameplay screen. Reminds me of a symbol that shows up on monsters when you use the Study Prey skill in the Hunting skill tree (from a previous playthrough). This is a skill that lets you "study" a monster (or group) to find their weakspots, and use of this puts a similar (same?) symbol next to the affected monsters for a short bit. But this one shows up next to the player's character and pets, and I'm not seeing any particular caster causing it; happened last night against your garden variety Satyrs. There might be an area of effect since I had one instance where it was coming and going on me as I moved around but it stayed solid on my Fire Elemental that was going hand-to-hand. Also, doesn't appear that it's some % chance effect from the Elemental.

Mostly a curiosity. I didn't notice that we were faring any better or worse while the symbol was present.

That's likely it, then. Centaurs were one of the monster types around that part of the game. Probably got the spell off before we toasted them.

Maybe I'll fire up the game on the other laptop, since that character has Study Prey.

Thanks.