Most of the ones I receive are from retired Dentists (It used to be mandatory to have a real skull to use in dental school) or are retired college teaching specimens. Many that I get have stamps from the medical companies that prepared them, and some have writing such as “Anatomy Dept.” or something similar on them. As long as they were obtained legally, they’re completely legal to own and sell, with a few exceptions:

There are 3 states that have restrictive laws regarding human remains:

Louisiana: Owning human remains (with exceptions to teeth, fingernails, gall stones, or cremated remains) is completely prohibited. This means you can not own ANY human bones if you live in Louisiana.

Georgia and Tennessee: In these states you can own, buy, sell, and trade human remains within the state, but you cannot import or export any parts in or out of the state. This means if you live in Georgia or Tennessee and want to buy a human skull, you will have to find one for sale within your state, and if you ever move out of the state, you legally cannot take the skull with you.