I'm not worried one way or another about an index on a CHAR column. However, storing numbers in string columns is very concerning. You're going to hit issues when you go to manipulate or retrieve those values if you attempt to treat them as numbers. Further, if you treat what's stored as a string as a number instead, you will get index scans where you should see index seeks. These will be caused by either your explicit or SQL Server's implicit conversion. That may make the index seem useless when, in fact, it's the code.