What are your ideas on the Mark of Athena? I know somepeople will probably get upset with this, but I still belive that Hera is going to have a kid and she/he is the seventh demigod. And who says it has to be like genetically her kid. It could be a orphan she snatches up (thanks BullyFan) and gives her blessing. But what about you guys?
Oh yah, it is also a fact that in the original Greek Myths Athena was supposed to be born with a twin brother who was supposed to overthrow olympus. Maybe he's Athena's bane, explaining the Mark of Athena.