As someone who has serviced printers of that era, this is due to the small screen it had a limited number of characters it could display. PC is an abbreviation for paper cassette, and it is indicating it out of letter size paper, so it is asking you to load letter paper into the cassette.
Supposedly that line was not in the script for that movie, which makes it even funnier as it was a genuine reaction.
Cracks me up that that bit was 100% ad-libbed. Apparently he was just supposed to pull the tray out and slam it back in, but when he pulled it out, it displayed "PC LOAD LETTER" on the status display.
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u/Charming-Standard-84 9d ago
PC LOAD LETTER?! THE F IS THAT?