Are you using the Staff Notes plugin? That provides links to all Official Warnings that a user has, which allow moderators access. I’ll grab a screenshot once I’m back at a computer.
OK, here we go. Sorry for the delay @JagWaugh:
Screenshot of a topic with a user who had an official warning (circled):
Staff Notes UI (Title of PM in blue):
To be 100% clear, that icon and the corresponding UI only appears to site staff. Official warnings are added automatically, any staff user can add a custom note as needed.