All 4 Uses

Morse code
in
The Three-Body Problem
(Auto-generated)

Wang saw that the page was nothing more than a Morse code chart.†
p. 92.3
After hanging up, Wang sat in front of his computer and printed out the simple Morse code chart.†
p. 94.1
Wang grabbed the first page as soon as it came out of the laser printer, and, with a pencil, began to match the distance between the peaks with the Morse code chart he took out of his pocket.†
p. 124.4 *
In the distance, the red star atop the Beijing Exhibition Center's Russian-style spire reflected the light from the cars passing below, also twinkling randomly.... Wang tried to interpret the flickers as Morse code.†
p. 128.1

Definitions:

(1) (Morse code)
a code in which letters and numbers are represented by strings of short and long signals such as dots and dashes

Originally used for telegraph messages and still in specialized uses today where a non-computer assisted code is desired. Perhaps the most innovative use of Morse code is when an American prisoner in the Vietnam War was forced to give a delayed-broadcast television interview. Unknown to his captors, while talking, he blinked his eyes in Morse code to spell out the word "T-O-R-T-U-R-E" and other messages.
(2) (meaning too rare to warrant focus)