Law enforcement can seize any type of property. They can seize physical property like cars, boats, weapons, cash, drugs, drug paraphernalia, houses, and other real property. They may also seize non-physical property such as bank accounts, royalties, and proceeds from crimes. They can even seize property that does not exist yet, such as the future proceeds of crimes that have not yet been earned when the crime takes place. Police may even be able to seize income a person later earns through book or movie sales from a memoir written about his or her supposed crime, although there is some question as to whether that would be a violation of the person's constitutional rights.
In our example, Officer Potts would argue that he seized Steve’s cash because Officer Potts believed that the cash was payment received for an illegal drug deal