Numbered Musical Notation
en.wikipedia.orgPersonal story: Some of my relatives in Thailand play the piano or electronic keyboard as a hobby. Almost all their "sheet" music score books are printed in this notation, but some of my western friends didn't realize it was music at first until they saw the lyrics.
Later on, I learned that country music in the US uses a somewhat similar "Nashville System" [1], but I believe that system doesn't let you span multiple octaves the way this system does.