The IRS requires that anyone who prepares or assists in preparing federal tax returns for compensation must have a valid Preparer Tax Identification Number (PTIN) before preparing returns. This allows the government to track tax returns by preparer and, in my opinion, has resulted in the decrease of fraudulent or abusive tax returns.
In prior years the IRS charged a fee for the PTIN but federal court ruled the dee to be illegal in June 2017. The IRS temporarily stopped the issuance of PTINs but is now issuing them again. A preparer should protect the PTIN from unauthorized use.
I renewed my PTIN for 2018. The number is automatically printed on all tax forms that I submit to the IRS.