No. no special signs all they have to do is post it.
TITLE 21 § 1290.22. Business owner’s rights BUSINESS OWNER’S RIGHTS A. Except as provided in subsection B of this section, nothing contained in any provision of the Oklahoma Self-Defense Act, Section 1290.1 et seq. of this title, shall be construed to limit, restrict or prohibit in any manner the existing rights of any person, property owner, tenant, employer, or business entity to control the possession of weapons on any property owned or controlled by the person or business entity.
subsection B states the property owner cannot prohibit the transport and storage of a weapon in a locked vehicle (The Parking Lot law).
This means if they post any no firearms sign on the door you can not take the firearm inside.