Files with mssign file extension are reported to be some sort of digital signatures.
MSSIGN file extension - Digital signature
What is mssign file? How to open mssign files?
File type specification:
The mssign file extension is used for files that contain digital signature that confirms the origins of other files located with it.
These files are often bundled with a product to validate the its authenticity.
This mssign file type entry was marked as obsolete and no longer supported file format.
This type of file is no longer actively used and is most likely obsolete. This is typically the case for system files in old operating systems, file types from long discontinued software, or previous versions of certain file types (like documents, projects etc.) that were replaced in higher versions of their original programs.