This may not be the right place, but it's the closest I could think of. Obviously, adding letters is a lot easier when all you need to do it to hold down a key on a keyboard, but I was wondering if there are any examples of it happening when people had to physically had to write down the extra letters?
Below are some examples of this or similar which I found, though it is up for debate whether they are examples of the same phenomenon, or something slightly different.
Example from 1954, "Best Sports Stories" by Irving T. Marsh, Edward Ehre. Here it appears to be used to emphasise "screaming".
https://i.imgur.com/29jDPNj.png
Example from 1972, "Confessions of a stockbroker", John D. Spooner. Here it appears to be more for sarcasm.
https://i.imgur.com/Qg0Hj87.png
Example from 1964, "Americans on Everest: The Official Account of the Ascent Led by Norman G[ünther] Dyhrenfurth" by James Ramsey Ullman. Here it appears to be used more to signal "calling out" to somebody
https://i.imgur.com/4DoJNs7.png
Edit: may have misinterpreted the question, sorry. For some reason I answered as if you'd asked "before the age of the Internet" ie before these would have been used in digital communication. But you said "before computers were popular". Taken literally, that could still mean "before ~1981", when the personal computer started becoming popular. But you may have had a different era in mind.
Follow up question, is there any evidence of this found in hand-written scripts, before type writers or any kind of writing assisting tools were invented?
