Unfortunately, after reviewing the GroupWise Token APIs, it does not appear possible to identify the current signature preferences. The preferences appear to be stored in the account, which makes sense, but means you cannot use a work-around like reading the Windows registry.
You can use the Token API command PrefSignature to set the signature options. The following is taken from the Formativ Language Guide.
Sets the signature that is appended to every message sent. Version: GroupWise 5.x and later.
GroupWise.PrefSignature(SigOptions eInclude, AddSignature Boolean, AddVCard Boolean, SignatureText String)
Specifies the signature include option.
Return notification options.
Only available in GroupWise 5.5 and later.
What do you wish to achieve?