After applying GDPR to a file as well as its GDPR expiration date, there are multiple ways you can see that GDPR has been applied through Collavate. In doing this, you can see whenever you are dealing with a file that contains sensitive information.
You can see when users in your domain have applied GDPR by going to the Home page then accessing the File Feed Menu > My Drive Activities.
In addition, when selecting files for processing or posting, you will be able to see which files have GDPR when you choose files from My Drive
Lastly, when users post about a file that has GDPR applied to it, you can see the flag in the post content as well as in the comments.