I don't know if this is rare or not, but I've never seen anything like that. I found a SONIC.SCR file in the root directory of the Sonic 3D Prototype I recently released. Basically it's a CD-R burner script. It seemed really cool to me. Edit: It didn't paste in the post so well. I uploaded it -> http://trash.drx.pl/SONIC.SCR
Its a file for Segas Virtual CD tool. Looks somewhat like a cue file.. Theres a manual for some sega cd related tools (including the one to burn your sonic) here: http://www.eatsushi.org/content/console/saturn/official_sega_docs/ST-129-R2-SP1-061995.pdf
Damn, you beat me to it! Yes, s1xty is quite right - that's the script file used for preprocessing in the Virtual CD.