Upon the Building Inspector's determination that the structure is unsafe or in a collapsed condition, notice shall be served upon the owner of said structure, or on the owner's executor, legal representatives, agents, lessees, or any other person having a vested or contingent interest in the same, either personally or by registered mail, addressed to the last known address, if any, of the owner, or on the owner's executors, legal representatives, agents, lessees, or other persons having a vested interest or contingent in the same, as shown by the records of the Receiver of Taxes and/or in the Office of the County Clerk or County Registrar.