Maybe there is even an easy way to do that but here is what I just figured out looking through all the properties of my Content Types.
When a Content Type is inherited from a Content Type Hub then the property SchemaXmlWithResourceTokens looks like this:
<?xml version="1.0" encoding="UTF-8"?>
<ContentType ID="0x010100EED4D9C563FDC1408AC154B300E928EE" Name="aaa" Group="Custom Content Types" ReadOnly="TRUE" Version="9">
<Folder TargetName="_cts/aaa" />
<FieldRefs>
...
...
</FieldRefs>
<DocumentTemplate TargetName="" />
<XmlDocuments>
<XmlDocument NamespaceURI="Microsoft.SharePoint.Taxonomy.ContentTypeSync">
...
</XmlDocument>
<XmlDocument NamespaceURI="http://schemas.microsoft.com/sharepoint/v3/contenttype/forms">
...
</XmlDocument>
</XmlDocuments>
</ContentType>
The important thing here is the line:
<XmlDocument NamespaceURI="Microsoft.SharePoint.Taxonomy.ContentTypeSync">
That seems to indicate that the Content Type is coming from the Hub.