When I visit the C:\$RECYCLE.BIN on Windows 10, I can see not only a link to the Reycle Bin but also two other directories, which I cannot access. Upon taking ownership of one of the directories and giving myself full permissions, it no longer appeared as "S-1-5-18", but as another "Recycle Bin". It only reverted back to "S-1-5-18" once I changed all of the settings back and toggled the "read-only" attribute.
What are these additional directories, and why do they display such unusual behaviour?
While this solution covers the recycle bin in-depth, it doesn't really provide an answer to exactly what you asked.
The $RECYCLE.BIN folder is essentially the master recycle bin within a Windows operating system, and the subfolders that contain a user SID (such as S-1-5-18 for the built-in SYSTEM account) represent the recycle bin associated with a particular Windows user profile residing on that local computer.
For a practical usage example, on our domain where I work we have shared computers where several users will typically delete very large files but inadvertently leave them in their recycle bin. If the hard drive on one of those machines happens to run low on disk space, we open an elevated command prompt and execute the following command to reclaim all of that storage:
rd /s /q c:\$Recycle.Bin
Following a reboot, the $RECYCLE.BIN folder will be recreated and each Windows user profile will now have an empty recycle bin.
