Logo

PhiCorp used the letter Phi as its logo. (TV: The Gathering)

The Fifth Doctor recalled that his book series was to be named with a comma, The Doctor, Who Discovers but became Doctor Who Discovers after "some idiot" in the publisher's design department missed the "The", creating a logo that said Doctor Who. (AUDIO: The Kingmaker)

Information from invalid sources
The TARDIS once flew through the Doctor Who logo, leaving a line behind it, striking through the logo. (NOTVALID: The NEW Doctor Who Logo)