Dalek writing

The Daleks had a form of writing.

Overview
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)

Post-Last Great Time War Dalek markings
The Daleks from the Last Great Time War, some groups of which survived its climax, had markings below the eyepiece. Later Daleks that were part of the New Dalek Paradigm lacked these markings. (TV: Victory of the Daleks)
 * While the exact purpose of these marking is unknown, they may be a form of identification or rank insignia.