By default, VB Migration Partner uses the /keyfile option when running the TlbImp and AxImp .NET utilites behind the scenes, which causes all interop DLLs to be always signed. The .snk file used to sign these DLLs can be found in VB Migration Partner’s installation folder (TlbImp_AxImp.snk).
You can replace this file with any other file with same name, if you prefer to sign these assemblies with your company’s public key. (Use the SN.EXE .NET utility to generate .snk files.)
In general, there is no reason for not signing interop DLLs. However, if by any chance you’d prefer not to sign these DLLs, you should either delete the TlbImp_AxImp.snk file or overwrite it with a 0-byte file. (If delete the file under Microsoft Vista, then VB Migration Partner’s install procedure would automatically restart and complain about the missing file.)
The simplest way to create a 0-byte file from inside Windows Explorer is using the New-Text File command and then rename the text file that you obtain.