You didn't say what state you are in but here is the law in Ohio.
G) A licensee shall not advertise or alter any informational part of a listing of any property, that is not listed for sale, lease, or exchange with the licensee's broker or brokerage, unless:
(1) The licensee has first secured written permission of the owner or the owner's authorized agent and fully discloses in the advertisement the name of the listing broker or brokerage as provided in paragraph (G)(2) of this rule.
(2) Where such permission is granted, a licensee advertising property, that is not listed with the licensee's broker or brokerage, shall disclose that fact, in the same or larger size type as the type used to describe the property, and the name of the listing broker or brokerage.
(3) For purposes of this division, the term alter shall not include limiting informational parts of a listing, provided that by such limitation, the information is not inaccurate or misleading.
So my understanding is that you can advertise it as long as you have written permission from the other agent and you advertise that it is listed by them and their brokerage.