What are the symptoms of an allergy to cats if you usually are fine with cats, but got hives visiting another cat?

Depends. Most typical allergic symptoms to cat are nasal, like hay fever, or asthma. There may some species that may cause more severe symptoms. One can have hives with contact to dander or saliva, or may possibly be a sign of a more severe reaction. If symptoms begin without seeing or touching the animal, allergic sensitivity may be quite severe.