If your organization do not want Outlook to use roaming signatures, you can disable the feature by creating/updating the DWORD value in the registry.
REG ADD "HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Setup" /v DisableRoamingSignaturesTemporaryToggle /t REG_DWORD /d 1 /f
If the key do not exist or the value is set to 0, Outlook will use the roaming signatures. The command line will create or override the current value to 1 to ensure that the roaming option is disabled and you can still use/update your signatures.
To execute the command:
1. Open "Command Prompt" as administrator.
2. Type or paste the command line and press Enter key.
Once it says that the operation completed successfully, the key is already set. You can confirm by opening your Registry Editor.
You can also copy the command line in a notepad TXT file and save is as .BAT to create is as batch file.