I am working on a concept around this topic and would like to clarify its meaning before designing a solution for it.
Are there existing definitions of the terms "user attribution"? What is it really?
I would define user attribution as:
The process of granting a user attribution of origination, authorship, ownership or any other associated right in relation to a specific piece of content.
I would suggest you look at the creative commons project for an example of how the process of attribution can be explored.