Domestic cats may have scars for a variety of reasons. It is therefore impossible to give an accurate answer without an examination and background history of the cat with the scars.
A cat with scars on its neck likely had an injury of some sort at some point. Cats that have spent any time outdoors are especially susceptible to injuries because of their extremely territorial nature, according to HowStuffWorks. Whether the cat fought with another cat or another animal, it is entirely possible for the cat to become injured in the fight. Sometimes, cat owners do not even know that the cat is injured until they find a scar. If the cat was adopted from a shelter, it is possible that the scar is the result of abuse or neglect from the cat's previous owners.
When a cat owner finds that his pet has scars on its neck, a trip to the cat's veterinarian is necessary to determine whether the scar has any lasting effects for the cat. The veterinarian may not be able to pinpoint exactly what caused the scar on the cat's neck, but he can determine whether there is a medical reason for the scar that may need to be treated. The ASPCA recommends that cats be kept inside to keep them safe.