A unique series of letters and/or numbers assigned by a property manager that will be used on all transactions to identify the original property management agreement is called:

The identifying code is a unique series of letters and/or numbers specifically created to facilitate the identification of an original property management agreement in all transactions related to that agreement. This code streamlines processes by providing a consistent reference point for property managers, which helps ensure accuracy and efficiency in record-keeping.

Using an identifying code minimizes confusion and assists in organizing and tracking various agreements, making it easier to retrieve specific documents and maintain compliance with management standards. In contrast, a security deposit account refers to funds set aside to protect against tenant damage; an employee identification number is related to staff rather than property management agreements; and a clients' trust account number is designated for managing client funds, rather than serving as a unique identifier for specific agreements. Thus, identifying code is the most appropriate term for this function.