Found a way to do this with a registry key.
the key is located at
HKCU\Software\Microsoft\Windows NT\CurrentVersion\Windows messaging Subsystem\Profiles[OutlookProfilename]\9375CFF0413111d3B88A00104B2A6676
in that key there will me mutitple folder 00000001 going up, for each signature one.
if you delete someone's windows profile the count starts at 1 again.
in here if you place a REG_Binary named
"New Signature" or "Reply-Forward Signature"
the value should be the name of the signature in hex format.
Say the signatures name is Test it would become
54 65 73 74 in hex. the reg key would like it like this:
54006500730074000000000000000000000000
i hope i made myself clear like this :D it wasnt easy finding this :D