StackOverflow just introduced the developer stories. When filling out your own story, you have the possibility to add a logo for each position (in a company) you held or each institution (e.g. your university) you studied with. You can see this in the link provided, where in one of the pictures the logo for the Yale University and the Vassar College have been used.
Is it legal to use logos in this situation without asking for permission? Does this depend on the country the company or the website is residing in?