I had the same problem with my CA-9200. Chris said there was supposed to be an on/off label.
Surprisingly (to me anyway) he e-mailed me: "its possible the label fell off. If that's the case you will have to plug the mics in and use your breath to figure it out sorry! because there is no standard side". I found it surprising that there wouldn't be a standard side. The right side was off on the CA-9100.
I wasn't exactly sure what he meant, but I held the mics about 18 inches from my mouth and blew into them as hard as I could. When the switch was one way the levels easily went over 0 db and when the switch was the other way they peaked at -6 dB or so. I assumed that the position where the levels went over 0 dB was off.
In my case, left turned out to be off, unlike the case with my CA-9100.
It does seem to be a great pre, though, although I haven't had a chance to use it in the field yet.