rel=”logo” is a proposed standard for serving and maintaining up-to-date logos for use in various media. By including a line of code on your site that links to a scalable vector logo, you make it very easy for other websites, applications, readers, clients, and stations to ensure that they are using an approved logo directly from you. rel=”logo” is a link relation tag, much like commonly used icon tags favicon or apple-touch-icon.
Logo-only seems such a waste - there is other, basic information (address, contact, etc.) that really needs to be part of something like this.
(via @eaton)