GPO to disable the import of digital signatures

Hi everybody,

I searched very long for GPO or a registry key to disable the import of digital signatures. I mean the option USE A DIGITAL SIGN FROM A FILE under the tool/certificates/digitally sign/configure id. I found the registry key to forbid the option "Create a new digital ID", but until now it was impossible for me to find the right key to disable the other option.

Does anyone have an idea which key could be the right one for the desired result?