Telegraph Talk and Talkers (1902) (books.google.com)

I think the anchors got trimmed off the URL, so this URL doesn't point to the correct page anymore. Page 227

-a ) check out Leo Marks' "Between Silk and Cyanide", which touches on a telegrapher's signature 'fist' - they were distinguishing between different (German) senders of coded messages over the air.

-b) this is still relevant today for (especially amateur radio) morse code operators

LL commentary: https://languagelog.ldc.upenn.edu/nll/?p=67333