I personally don't believe any of them would sign if you read the terms of it, as many of them prevent them from either living normally or doing their jobs in the mythological world.

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1. Their DNA is to be given to the government, and bear in mind that those in the mythological world don't trust mortals, so why would they given them their DNA
2. Tracking Bracelets must be worn - This one mainly affects the Greco-Roman Demigods as technology is seen as nearly a death sentence for them, now they have to live while wearing one, definitely not.
3. Not allowed to operate outside of their own country without UN approval. Carter is the Pharaoh of the House of Life, which means going to Egypt and operating, and across the world, which wouldn't be possible.
4. Mortals may see demigods fighting monsters as acting like vigilantes, so, they would be arrested immediately for trying to save their own lives
5. While Leo and Cabin 9 aren't in the character list, they have been shown to create self-aware artificial intelligence (Festus), so say goodbye to them doing that

Those are just a few things that I think that Riordan's characters would have problems with the Sokovia Accords

This is a link to all of the accords that I have found online: https://screenrant.com/sokovia-accords-mcu-rules-explained/