Leitz put 'feathered' arrows on the advance and re-wind knobs of Leica 1s for a limited period from late 1926. The majority had three 'feathers' or six if you count each line separately. A limited number had only two (or four) 'feathers' on the advance knob arrow only for some unknown reason. Lars Netopil says that this is a rare variant, and I have only come across three: serial #s 3293, 3520, 3564. Despite these being in the 3000 range Mr Netopil has not come to any conclusion about the serial numbers from the few he has also seen in the past. Angela von Einem tells me that the 'triple feather' arrows were embossed (geprägt) but says the 'double feather' on camera #3520 is engraved. It is indeed much clearer than the usual rather blurred arrows on other cameras.
I wondered if any members have 'double arrow' Leica 1s in their collections, or have come across any. Serial numbers would be very helpful. I have attached a photograph of #3520.