The Ghorfa petroglyphs were a form of writing system used by the ancient Ghorfas on Tatooine up until 5000 BBY, when Human colonists caused their culture to wither away.
This writing system consisted of elaborated pictures and seemed to have been logographic in nature. When the Ghorfas evolved into the Sand People, their complex pictural writing devolved into a series of crude symbols. Eventually, the Sand People came to rely exclusively on oral history.
When a young Luke Skywalker and his friend Biggs Darklighter set off on an archeological adventure and discovered the lost city of the Ghorfas, they came across tombs that were engraved with such writing. Several of these tombs allowed them to understand a very clear story of the Ghorfa civilization's decline. With proper translation, those glyphs would mean : "With thunder, the spaceship came to the land. We came to our well and the water was gone. And so he died of thirst. May his spirit watch us so that someday, there will be death to the spaceship that steals life, and there will be water in abundance, and we will have our revenge."