How to include list of items into certificate?


We want to include list of specific entries into certificate.
Lets say entries using following schema
{“id”: 1, “name”: “item 1”},
{“id”: 2, “name”: “item 2”},
{“id”: 3, “name”: “item 3”}

Can you please advise what Blockcert property we should use for this?
What is the purpose of badge.signatureLines? Documentation( doesn’t cover this property, but it is used in test certificates.
Or maybe define custom property. Are custom properties allowed by Blockcert standard?

Thank you!