Objects in S3 can have custom metadata associated with them. Look at the returned data for the HeadObject call.[0]

It's not advertised in the documentation, but HeadObject(Bucket, Key)['Metadata'] is a neat dictionary of custom values.

0: https://docs.aws.amazon.com/AmazonS3/latest/API/API_HeadObje...

S3 supports metadata (see https://docs.aws.amazon.com/AmazonS3/latest/user-guide/add-o...).

Perhaps I don't understand what you're saying fully though--as I don't fully understand your comment.

You mean like Object Metadata for S3?

https://docs.aws.amazon.com/AmazonS3/latest/dev/UsingMetadat...