Signature presence

A signed .3mf carries signature files that tie it to a certificate.

What does preslice check?

Whether the archive holds signature files, such as _xmlsignatures/ or a .p7s. The 3MF Consortium publishes the signature extension at 3mf.io/specification.

What does the result mean?

It only says whether signature files are there. Most files are unsigned, and that is normal.

Why not verify the signature?

That needs a trust decision about certificates. Use a tool with your own trust store if authenticity matters.