How to tell if content has been migrated I am using drupal2drupal migration. How can I indicate that some content has been migrated as opposed to being manually added.
You could alter the incoming data and attach a taxonomy tag, like 'migrated', to indicate this.

You could also add (migrated) in the title, but you would have to ensure this does not affect users, terms, URL aliases, etc. Hence why I suggest a taxonomy term. I am not that familiar with D2D API but I know this is very easy to do with Migrate Framework.