In the "When Will You Rage?" anthology (classic WoD fiction), background characters are referred to as having a red left eye. I also seem to remember this particular bit being brought up in other pieces of White Wolf fiction, although I haven't read them recently. However, I can't find any information on what it's supposed to mean. Is this a reference to a particular template? Or some sort of supernatural event? Where is this explained?
From the "When Will You Rage?" anthology:
The redhead was bothered by some people he had seen on the street. A few had a single red eye, always the left one. He had never seen anything like it. Bunny eyes, he called them.
He ignored the Halloween decorations, the children dressed in costumes and being dragged around the area by their parents — all save the odd child in the Terminator mask, the one who's left eye glowed red. That one had walked right up the side walk, just as happy as any of the other kids on the street, had even waved at Samuel where he was perched in the shrubs. No one was supposed to see him, strange eye or not, and Sam took the hint and moved to a better position a few feet away.
It's possible this is just a quirk of the novel, so if someone who's read (at some point, not asking anyone to reread) all the W:tA sourcebooks published prior to the anthology can confidently say this isn't mentioned in any of them, I'll go ahead and accept that answer.
NOTE: A good answer to this question should be along the lines of, "A red left eye means A, as explained in source book B." Alternately, an answer saying, "A red left eye has no special meaning in the general WoD setting, and is instead a bit of flavor used by author C, who wrote those particular stories," would also be OK. "It's probably D," is not a good answer, unless you can provide a specific rulebook quote referencing red left eyes to back it up.