Driver signing for generic PS based driver (pscript5.dll+PPD)

Hello group,

my company is deploying a application which uses a printer driver which is
based on Microsoft's (or Adobe's as you like) generic PS printer driver
pscript5.dll.

When installing "our" driver, we get a warning, complaining about the driver
being not signed.

Do you really have to get a simple PPD signed by WHQL?
Or do we make a silly mistake when installing it in our setup script?

Any help to avoid that warning message would be greatly appreciated.

Thanks in advance,
Markus Woessner