SYM (file format)
From GICLWiki
Extension: .SYM
System: CADENCE/VALID ALLEGRO
Description: Bare Board net list, Board drawings are .brd
Extension: SYM
Program and/or Extension Function: P-CAD Component Symbols
Company: Altium Limited
Specific Notes: (None)
Identifying Characters: (None or Unknown)
Program ID: (None or Unknown)
General Notes: (None)