I believe it would show up as magical, but as written it has no school. However, I would tell players it "looks similar to the Necromancy school, perhaps some kind of curse..." As for Aura, I'd go with the Magic Item section, using the Witch's caster level.
It doesn't. It is not a spell or magic item, and has no spell level or caster level (hexes that vary by level, such as healing, have to state specifically that they use the witch's caster level).