From versions v1.14.4 of the Schema App Structured Data plugin we add a "data-schema" attribute on the script tag to denote the source of the schema markup.  You can use this to identify the origin of the schema data, as well as other aspects of the page.  The following is the structure of the attribute: 

  1. Post Id
  2. Post Type
  3. Type of schema markup (Default, Custom, App)

Example 1: Shows a data-schema value for Post ID 17, Post Type "Page", and it comes from the Application:

<script type="application/ld+json" data-schema="17-page-App"> ... </script>

Example 2: Shows a data-schema value for Post ID 18, Post Type "Post" (a blog post), and it is default plugin markup:

<script type="application/ld+json" data-schema="18-page-Default"> ... </script>

Example 3: Shows a data-schema value for Post ID 19, Post Type "Post" (a blog post), and customized in the plugin:

<script type="application/ld+json" data-schema="18-page-Custom"> ... </script>

Similarily, the schema markup data for the Website is set to data-schema="Website" whereas the Breadcrumb item is data-schema="Breadcrumb". 

For versions v1.14.3 and earlier, we used a HTML comment block before and after the schema markup. However, caching and website performance appliances often strip HTML comments from the source.