Cats are by nature hunters and can be poisoned just by catching and eating poisoned animals such as mice or birds. Things to look for are lose of appetite, neurological problems, paralysis and vomiting. Pets have also been poisoned by anti-freeze. The best thing is take your pet to a vet to be checked.
Anything odd with the cats personality or health is a good indicator that it is sick or poisoned. If you look in your cats litter box and see if the feces is a different color or texture than before. Blood coming out of anywhere is an obvious sign. Also if the cat is balding or has odd fluids secreting.
The cat may have seizures or severe vomiting. He may be extremely agitated. Other signs are tremors, drooling and paddling of the legs. If you suspect poisoning, get the cat emergency treatment right away to avoid damage.
Your cat will probably look lethargic and may not eat or drink. If you suspect someone has poisoned your cat take your cat to the Vet right away. They can take the proper precautions to save your cat's life. If you wait too long your cat could die from the poison.