I have a '66 360/12 in Fireglo that I've owned since 1971. It has a major mystery that I will post later this evening after I've taken photos, and a minor mystery that I will describe at this time. With the pickguards removed, there is a very clear mark written on the inside of the back (unfinished) surface that reads as follows: "360-12-M". My first guess is that the "M" stands for Mapleglo and that my guitar ended up with a Fireglo finish despite its having been designated to get the Mapleglo finish. Good guess or does the "M" have another meaning?
The major mystery (teaser alert) has to do with some mysterious (clearly non-factory) holes drilled through the pickguards and into/through the front surface beneath. If I get the pics done this evening, I'll post under a new topic.
Looking forward to your replies.

The "M" would likely have been only a marking by the factory or finish department manager, a personal code to help him determine when the instrument was final coated so that he would know when to put it through for buffing.

You'll see many marking over the years that really have no universal meaning. Sometimes it's just an initial of someone who worked on the guitar.

Thanks, Mr. Hall (may I call you John?). Interestingly, there's a photo of what looks to be a similar vintage 360/12 on the homepage of a local luthier (www.oldschoolguitar.net) that shows a nearly identical inscription except that it reads "360-12-I". That guitar appears to be Mapleglo, confirming your surmise that the letter designator isn't a color code. A daily or weekly sequence perhaps?
Anyway, I join many others on this forum in thanking you for you personal involvement and for the obvious pride that you take in your company, its employees and its products.

I am brand new to Rickenbacker having recently acquired a 2014 360/12. I cannot put it down. It's everything I thought it would be. I noticed a signature under the pickguard. Perhaps whoever applied the finish signed it? It is difficult to read but it appears to say "Gamer Stumpf." I like the idea that the artist signed his/her work. Any insight on this Mr. Hall? Here is the link for the image: http://imgur.com/iyKqwyz

it looks to me that it says "Carmen", not "Gamer".