> All fields that hold paths in the manifest must be absolute paths (for example, /images/myicon.png), and the paths must be served from the same origin as the app.

— https://developer.mozilla.org/en-US/docs/Web/Apps/Manifest#Path_handling

I don't think the logo could be on S3. But Rails may render this file or it could be a data URI. (https://developer.mozilla.org/en-US/docs/Web/Apps/Manifest#icons)