As an administrator, you can create signatures for users based on a template (PSA_RPT_EMA_SIG_...) for the "Signature" object.
The Signature function is available in the user administration. The dialog for the function shows the signatures already present, also those that internal employees have created under My Data. For a new signature, select a template using the Create button, assign a name and set the Global, New and Reply flags if required.