The Daleks had a form of writing.
During the 22nd century invasion of Earth, the Daleks placed notices around London locations with uncertain meaning. (TV: The Dalek Invasion of Earth)
Dalek writing was displayed both on screens and in the vision of certain Dalek factions. (TV: Remembrance of the Daleks)
Daleks that originated from the Last Great Time War possessed markings below their eyepieces for identification. (TV: Dalek, The Parting of the Ways, Doomsday, Daleks in Manhattan, Evolution of the Daleks, The Stolen Earth, Journey's End)
The War Doctor could understand Dalek writing, to a degree at least, and was skilled at hacking into the Daleks' databanks. (PROSE: Engines of War)