Unlicensed jars, while not being as hot a topic as reproduction jars, still must be given consideration. Not all makers are spending the money to license jars, while others are. If this is an important issue to you, be sure of what you are buying before you make your purchase. Whatever your thoughts may be, education still remains the best weapon in your collecting arsenal. Everyone talks about education.
Colors are a clue too, as is the size of the jar.
Most reputable cookie jar dealers will answer your questions and even give you pointers on the books available. Be a student and study these books, it will help make you a more knowledgeable collector. You won t see the books as expensive the first time they help you determine what you are buying and perhaps save you from an unwise purchase. Many folks find rubbing elbows with other collectors to be a boon. You can learn so much, not to mention the thrill of seeing the collection.