Found some info:

How do I pick which letter prints with the return?

With more then one letter to choose from you can now customize what letters print with the return:

1. Open a client.
2. From the File menu, select Print Options.
3. From the left side of the screen, select Control Which Letters Print. 
   • Here, you can customize what letter prints with each specific copy of the return.
4. Click OK to save your changes.