Skirt Guards are common on bicycles in continental Europe, where the bicycle is commonly ridden in smart-casual or formal clothing; but very uncommon in English speaking countries where many cyclists wear specialised cycling gear. It is often paired with a chain guard to keep the rider's clothing clean. They are often used on utility bicycles.
There are several forms, for instance -
Solid plates have the disadvantage of air resistance, which increases the risk of being blown sideways by gusty sidewinds. Air-permeable designs such as mesh and string provide a more stable ride, but can be more difficult to keep clean.