The entire fandom agrees that Percy Jackson has some scary eldritch qualities that humans notice. But I think that all the demigods do, even if most of the effects are more subtle. Powerful demigods are super noticeable, but even the weakest are scary to normal people. But I like to imagine some of my favorites:
Annabeth looks at people like she's dissecting a blueprint, and nothing about them is hidden. She turns her head at odd angles, like an owl. She notices small things and goes completely still, staring, like a bird of prey who just saw a mouse. People feel unsettled by her gaze, like every weakness and vulnerability are no longer hidden.
Hazel's hair, skin and eyes seem to shine metallic when the light catches just right. Sometimes her motions are rigid and awkward, like she hadn't used her limbs for a long time, like she isn't used to having a body. Her shadow is a deeper black than it should be, is bigger than it should be, and doesn't always move with the light.
Nico's skin is sometimes almost translucent, like he is more ghost than human. You can almost see the muscle and bones beneath it. His eyes catch and hold people, so dark and deep it feels like they are falling an incredibly long distance into dark water and earth. His shadow is also too dark. Sometimes, people swear they can hear faint screaming from his shadow, like thousands of tormented souls are trapped inside.
Jason has fangs, more wolf than human. His mouth opens wider than it should, and he looks at people like he is thinking of the best way to hunt and catch and rip and tear. His eyes are too blue and he always smells like ozone. People want to bow to him as he walks by. People want to run, but instinctively know that he will chase them, and they wait, frozen, for him to pass.
Thalia, like Jason, is a hunter. Her eyes are too blue, too vivid, and she stares people down like she is already picturing them riddled with arrows. She tracks small sounds with terrifying intensity. Brushing up against her will deliver a horrible static shock, and power lines and lights flicker and buzz when she walks by.
Will's hair is too bright. His skin glows, especially at night. At first, it seems to be a sweet thing, his good nature shining though. But sometimes when people touch him, they burn. Just standing near him is too much, like standing in the direct sun on a hot summer day.
Piper's face seems to change, every time someone turns to look at her. Subtle, but someone's subconscious is screaming that this girl is different, something is wrong. Her voice trills, like a bird, when she in happy. People can't help but to follow her and when she is gone, they feel bereft. She is too beautiful, and it hurts to look, but people can't help themselves and look anyways.
Leo is always hot to the touch. His fingers and limbs feel rough and metallic, his hair curls like wire. His eyes glitter like polished coins and when he walks by, cars and computers and machines start up and move on their own, just for a moment. He runs across a busy street and the cars stop for him with no regard for what the driver is doing.
Frank doesn't move like a human. He glides, slinks, pads softly and so quietly most people don't notice him. He had an aura of command. Frank seems so normal and average, but angry or upset people look at him and know that they can't take him. Sometimes, when he is angry, people get upset and fights start in his wake.
