“When is possession more than possession?” asked the court. It answered: “When an unconstitutional statute creates a legal presumption that possession means a great deal more.” Penal Code section 12090 prohibits change or obliteration of the identification marks of a firearm. Penal Code section 12091 creates a mandatory presumption that the possessor of a firearm with altered identification marks was the person who altered the marks. The court held the statute created an unconstitutional mandatory presumption by relieving the prosecution of its burden of proving the ultimate facts beyond a reasonable doubt. The court joined two other district Courts of Appeal in concluding that proof of possession of a firearm with an altered mark was not sufficient to prove the possessor was the alterer.