In Japan, '39' is common text speak for 'thank you', due to how 3 (san) and 9 (kyu) sound when spoken out loud.
Source
During the Cold War, CIA agents used a method of communication based on how their shoelaces were tied.Source
In Japan, '39' is common text speak for 'thank you', due to how 3 (san) and 9 (kyu) sound when spoken out loud.
Source