If you are in the South Island then it is unlikely to be Facial Eczema, so look out for cloudy eye/s and lots of tear staining. This is blindness caused by dust or a bacterium.
In the North Island, as well as blindness, you also have more likelihood of Facial Eczema is your paddocks are sheltered from the wind, and/or northerly facing, and/or further north and lower altitude,The most obvvious symptom is the ears peeling and shaking it's ears, and looking for shade. When it is really obvious the skin peels off the face. Often with sheep the visual signs are not very obvious because the liver gets the most damage. It has been found that for every one sheep that shows visual signs there are twenty that have liver problems. There is not much that can be done after the ruminant has FE.
If you find a sheep sitting in the shade & its shaking its head & scatching its head & ears & seems to be scaley it could be exzema. If you pull their ears & they shake their head it is likely it has Exzema.