Thanks for the chance to help with this. I am an attorney with over 12 years experience. Hopefully I can help you with your legal question.
Great question...the answer is that there is not any sort or required marking for intellectual property. A company can copyright
material (this involves applying to the federal government for copyright protection) or can apply for a trademark
(for a particular brand) or a patent
(if the material is suitable for patent). If this has happened you may see evidence of the branding or copyright (the TM symbol or "circle c" symbol).
But this is not always required. For example, it is possible for a company to generate intellectual property (like, for example a book, computer code, art, etc) and not apply for copyright protection. Copyright law will protect ownership regardless of copyright protection is sought.
But back to the question, if a company produces intellectual property (or, employees of the company produce intellectual property while working for the company) the company retains ownership of that property. They are not required to "mark" it...though they may well do so, depending on company policy. But whether or not they mark it will not impact their ownership rights at all