Would it be possible to create a column on a SP folder as a status indicator i.e. review completed.
SP Folders are treated just like any other list item for the purposes of adding and displaying columns. They also have the content type 'Folder', and if you enable management of content types in your library, you can add the column just to folders.
Enable content types and then use the "Extended Folder" content type. This content type allows the folders in your list/library to use the other columns you set up. The default folder content type does not allow you to add other columns like the extended one does.
Also note that the properties of the folder will not inherit to the items/documents stored within.