[1][2] Any organised collection of symbols and symbol-manipulating operations can be considered a data system.
Hence, human-speech analysed at the level of phonemes can be considered a data system as can the Incan artefact of the khipu and an image stored as pixels.
A data system is defined in terms of some data model and bears a resemblance to the idea of a physical symbol system.
Hence, the sounds of human speech are non-persistent symbols because they decay rapidly in air.
In contrast, pixels stored on some peripheral storage device are persistent symbols.