There are a couple different options to generate a Trademark symbol  (™) on a printed label.  The first example is directly placing the code in the PRN file.  The second is by getting code from a Spec Value.  

Further information can be obtained from the ZPL Help pages themselves: ZPL Trademark Help Page

Direct PRN Code.

This option will concatenate the Trademark symbol with the previous text entry value.  

PRN File Code:

 

Trademark via Spec Value