Stigmas are a very important part of the female cannabis reproductive system, they are the tiny hair-like strands protruding from the Pistil of the plant, specifically the Style, the end of the Pistil. These sticky hairs are what collect pollen from the male plant to pollinate the plant. When growing cannabis feminized seeds, there is no need for pollination, but the stigma serve another purpose.
Examining the color of these tiny hairs as they progress and get darker from yellow, to orange, to a darker red or brown depending on the strain is an indication of when to harvest your cannabis plants. They will also begin to curl up when it is close to harvest time.