Sega, unlike Sony, has never made special "debug" systems for testing betas. 
Debugging was done on the dev consoles and the testing was done on standard 
units with key discs. What you have is one of the key discs. 

The Saturn required a set of two key discs. One for third party games and 
one for first party games. What you have is the "Black" third party key 
disc. The first party key disc is the "Red" disc. 

In order to play a CDR on the Saturn you need to load the proper key disc 
and then load the CDR. The Black disc will boot any third party CDR while 
the red disc will boot any first party CDR. The system discs do not disable 
the county code check, they only disable the CDR security check. However, 
the system discs themselves are not country coded and will work in any 
system out there. 

Once the Saturn has been booted with the key disc, the CDR security check 
will remain disabled until the power is cycled. This was done to allow for 
multiple disc games as well as to allow for the swapping of different games 
without having to do the boot-disc cycle again. 

The Maker ID on the discs are unique to whomever originally licensed the 
discs, presumably to prevent them from being sold. 

Sega kept the same system with the Dreamcast, however only one system disc 
is used instead of two. Interestingly enough the Dreamcast system disc is 
labeled Dreamcast System Disc 2. I don't know if there ever was a System 
Disc 1 for the Dreamcast or if the 2 was to denote that System Disc 2 was 
for the DC while System Disc 1 was for the Saturn. 

What you have is quite rare and hard to find. However, most people don't 
know what the hell it is so when they do become available the discs tend to 
go cheap. I remember about a year or two back a Saturn system with a black 
disc popped up on eBay. Someone asked about it here on the list and I posted 
an explanation. I figured that it would go for a sum of money so didn't 
bother bidding on it myself. Heh, I was quite surprised when the package 
closed at around $75. Whoever got that (was it you Jason?) got one hell of a 
deal. Had I known it would have gone for so cheap I would have snagged it 
myself.