
Baron Sekkady was a master torturer and a powerful mage. It's heavily implied that he was a follower and a priest of Liart, who grants his followers magical powers for their prowess in torture. Because of this, Kieri has scars all over his body. He has a few on his face, as well. They're not detailed in canon; Kieri grew up to be a Captain of Falk (aka, a Knight) and then the leader of a mercenary company, which he ran for many years. As such, the adult is even more scarred than the child. Sekkady would have wanted Kieri recognizable, so I tend to assume the scarring on his face is not as heavy as it is elsewhere (such as his back).
He does have two of note on his face (it is mentioned that he came to the Halverics with scars even on his face, although they are never detailed). One is on the right side, running mostly vertically down his cheek. It's a bit jagged looking, as though the tool is was made with tore the flesh and didn't simply cut it. The other one is longer and higher up. It's a straighter cut, and finer. It was just deep enough and in just the right place to bleed heavily. It had been an unspoken threat, whereas the other had been one of many punishments Kieri has endured.
They are mostly covered by his beard, but they can still be detected if someone takes a close enough look at him.