In previous versions of SDL Tridion, you could add a logo to the Content Manager Explorer by updating the CSS (see my example on TridionDeveloper).
Specifically, you could add a
background-image to these CSS selectors:
.tridion .abouttridion .button, .tridion .abouttridion .button.mouseover, .tridion .abouttridion .button.mousedown
It looks like the .abouttridion class has been replaced with the personal information center.
I've left a comment on SDL Documentation, but what element would you recommend for adding a logo-type image to the interface?