Assign Letters Automatically to Files
Don't miss that Bulk Rename Utility can be used to assign letters to a set of files. In the Numbering section, click on the drop down menu for 'Type', which has 'Base 10 (Decimal)' as the default. Change the setting to 'A -Z'.
Set the 'Mode' to 'Prefix' and add a space in the 'Prefix' field in the 'Add' section. The utility will assign letters to the selected set of files: