What are common signs and symptoms of ischemia?

Depends. That would depend on what organ system is involved in the ischemia. If the brain, for instance, weakness of one side of the body, numbness, visual loss, etc. If the heart, then pain in the chest. Ischemia to the legs would cause pain in the legs at rest or on walking.
Definition: ischemia. The term ischemia generally suggests a reduction of the blood supply to a given area of the body such that the functionality of that part of the body is impaired. Could be from a blockage in an artery delivering blood to that part of the body, or could be from a general reduction in blood supply to deliver to that part of the body. Symptoms depend on location - heart, brain, legs, abdomen...
Depends. Any organ with ischemia is probably not working well and the product of that organ diminished. Heart-low cardiac output kidney failure brain stroke limb gangrene.