What are the visual signs of uncontaminated margarine spoilage?
Margarine should be stored in a refrigeration situation.  While not a safety concern, the main risk is rancidity.  This can happen as quickly as over night, if margarine is left out of the refrigerator.  Visual signs of quality degradation are a dark, hard, or waxy appearance. In this case, it might smell like soap or old microwave popcorn.  Also a possible sign of spoilage is water droplets on the surface of margarine (except if it had been frozen.  In this case it can be re-mixed.). Given the high concentration of saturated fat, margarine is a difficult medium in which to grow mold, which would be an indication of spoilage. Typically the mold is growing on bits of food left behind in the margarine.  In this case margarine might become a health risk and should be discarded. You can find more information here.  Safety is not about the type of emulsion, but the ingredients in the emulsion, the water activity in the system, and the storage environment.