I guess I wasn't sure where the line is drawn for advertising in need of licenses. If, in the post, I'm directing them to a website that offers paid services, I can see how I'd need a license for that. What if there's no such explicit advertisement? Do I need licensing regardless because it's on my company's account? It sounds like a better-safe-than-sorry scenario to me, anyway.
Owning a copyright comes with several exclusive rights. The owner of the copyright has the exclusive right to do and license others to do the followign:
(1) to reproduce the copyrighted work in copies or phonorecords;
(2) to prepare derivative works based upon the copyrighted work;
(3) to distribute copies or phonorecords of the copyrighted work to the public by sale or other transfer of ownership, or by rental, lease, or lending;
(4) in the case of literary, musical, dramatic, and choreographic works, pantomimes, and motion pictures and other audiovisual works, to perform the copyrighted work publicly;
(5) in the case of literary, musical, dramatic, and choreographic works, pantomimes, and pictorial, graphic, or sculptural works, including the individual images of a motion picture or other audiovisual work, to display the copyrighted work publicly; and
(6) in the case of sound recordings, to perform the copyrighted work publicly by means of a digital audio transmission.
17 U.S.C. section 106.
Using a copyright-protected song/sound recording in social media advertising would violate both the public performance and digital audio transmission rights. Copyright owners might let stuff like this go in random videos, but it's unlikely anyone of any consequence will let it go in advertising.