When O&O DiskRecovery opens, it automatically loads all user-defined signatures and adds them to its overall list of file types. Please note that all user-defined signatures must be located in either the O&O DiskRecovery program folder or in the 'My Documents' folder for the program to be able to successfully detect and load them.
If you have your own signature with an extension that either already exists in the master list of file signatures or has already been loaded in the past, it will not be loaded again and an error message will inform you of this.