I think the Finns created the portal stones. They probably have the capability to create the portal stones. And the Mark that Olver made in the air (a triangle with a wavy line) sounds like a PS mark. Also the Portal Stone worlds have different time scales, a day in one is a year in Rand's. What's to say that one isn't a world of the past and a world of the future, therefore allowing the Finn's to predict things. They can make things like the medalion, so the Stones might not be beyond them.

TITLE: Lord of Chaos, CHAPTER: 33 - Courage to Strengthen

"Well," Olver muttered, "we almost won. Another game, Mat?" Not waiting for an answer, he made the sign that opened the game, a triangle and then a wavy line through it, then chanted the words. '"Courage to strengthen, fire to blind, music to dazzle, iron to bind.' Mat, why do we say that? There is no fire, no music and no iron."

1) One mark is a triangle with a wavy line through it.

2)A triangle standing on its point in a circle was the sign for Randland

3)Two parallel wavy line crossed by an odd squiggle

4)Two triangles surrounded by forked lightnings, one ging left, the other right.

Also the portal Stones in trolloc world were twisted/curved column

The columns after Mat when in the first time were tall and twisted.