In Clarity go to Administration->Object->Task and click on the the 'ID' attribute on the Attributes tab
Click on the 'Auto-Numbering' tab
Check the check box next to Auto-numbered
To customize the auto-numbering algorithm click the Edit link under 'Scheme'. This includes the ability to add unique letters such as a T, in the beginning of the task ID.
To enable auditing for another object's ID, simply replace "Task" in Step 1 with the desired object. (Example: Project to enable Auto-Numbering for the Project ID field)
Note: If you are creating tasks in Microsoft Project (MSP), by current design, the auto-numbering feature is not available. You can enter the Task ID manually in the Text1 field to create a task ID for those tasks.