0.3 milliohms or 300 microohms.
You will often find the unit prefix used in place of the decimal point in electronics, be it on schematic diagrams, PCB silkscreens, or on the components themselves.
Supposedly it originates from the time when schematic sheets were hand drawn and copied back and forth. Degradation of image quality meant that decimal points had a tendency of disappearing, so the simple solution was to avoid using them entirely.