I have noticed with the large amount of optical drives and CD/DVD players I have taken apart that most of the spindle motors (RF-300, RF-310, RF-400, etc.) have the somewhat cryptic marking "D/V 5.9" on them along with the standard part number. This appears to be mainly found on spindle motors, and very rarely on the sled or eject motors. It also appears to be a fairly standard marking, as I have seen it on motors dating back to 1985. It could be the recommended voltage, although Mabuchi's information on the RF-300 says the voltage range is 1.5-6 volts and 3 volts is nominal. Some motors I have seen write "D/V" as if it were a fraction. All but 2 of the motors I have seen this on are made by Mabuchi, and on the ones that are not there is nothing after the "D/V" marking. I have been looking for an authoritative source on this for a while, and it seems there is none.
Any ideas about what it means or why it seems to be found only on spindle motors?