A siff file extension is related to the Scene Interchange file format developed by Sega. Probably obsolete format.
SIFF file extension - Scene Interchange file format
What is siff file? How to open siff files?
File type specification:
The siff file extension is associated with Scene Interchange file format, developed by Sega, in an attempt to create a establish a portable 3D data format in 1996.
Most likely some old format without support. No further information could be found.
This siff 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.