Short answer: Grawlixes are the various keyboard symbols that you find when pushing shift and mashing the number keys in order to produce nonsensical stand-ins for implied profanities.
I know I'm probably dating myself a little bit here, but do you remember that Sunday comic strip, Andy Capp? The basic premise was that this British guy drank entirely too much booze, stumbled home too late, and inevitably become ensnared in domestic squabbles with his long-suffering wife, Florrie.
Every time ol' Andy and Flo descended into heated argument, word bubbles filled with grawlixes. These grawlixes usually included some random combination of percentage symbols, dollar signs, exclamation points, ampersands and pound signs…Oh sorry, I mean hashtags (#lifebeforetwitter).
On the surface, these wingdings were essentially meaningless. But the wonderful thing was, even as a kid, I knew they were supposed to be swear words. And because they were not explicitly spelled out, I was free to elaborate on their profane intentions in my own imagination…which I can assure you was far worse and more unsuitable for general audiences than whatever the original cartoonist might have intended.
Andy Capp, as it happens, is still in circulation, and has been without interruption since 1957. In spite of Andy's binge drinking, he significantly outlasted his creator, Reg Smythe, who passed away in 1998. And to date, in spite of their obviously troubled marriage, Andy and Flo are still together, and still hurling grawlix-laced invectives at one another on a pretty regular basis. And we, as readers, are left to imagine the colorful North English profanities implied within.
I only mention Andy Capp because, the way I remember it, this was the swearing-est comic around when I was a kid. If grawlixes hadn't been invented, Andy Capp might only have seen the light of day in adult magazines, nestled between airbrushed centerfolds and coupons for things you wouldn't want your neighbors to see getting stuffed into your mailbox. Thanks to grawlixes though, Andy remains a fixture of the Sunday edition, modeling behavior for generations of snooker addicts and football hooligans.
So what was that liberating moment when cartoonists were given the subversive power to swear without falling afoul of society's moral hygienists?
An article in Slate credits their likely invention to a true pioneer in the cartoon business. Around the turn of the 20th century, German immigrant Rudolph Dirks landed a gig with the New York Journal, which began regularly featuring his illustrated panels. Calling his comic strip The Katzenjammer Kids, Dirks produced two of the most consequential innovations yet seen in cartooning. Foremost among them, his characters were the first known to speak to one another in word bubbles. Second, the word bubbles at times contained these symbolic vulgarities that—it would seem—readers intuitively understood as expressions of otherwise unprintable anger.
This intuition was aided by the fact that the young Katzenjammer protagonists, Hans and Fritz, existed largely to caper at the expense of their adult caretakers. Their comic strips frequently descended into either vain yelling or punitive spanking. In either instance, one might well be treated to a feast of punctuation marks and symbols. Slate points to a 1902 edition as perhaps the first of such instances. The Slate article also makes note that among the symbols included in this first primitive form of grawlix was an anchor, owing both to the nautical profession of the character speaking, and more subtextually, implying that said character was engaged in the act of “swearing like a sailor.”
In each instance, the context allows us to loosely surmise what the author intended by any specific invocation of grawlix. And increasingly, this became the convention, not just for Sunday cartoons, but for mainstream fantasy, monster, and superhero comic books as well. That said, the edgy symbology lacked a particular name until 1964. It was then that Mort Walker—author of classic Sunday funnies, Beetle Bailey (1950) and Hi and Lois (1954)—coined the word Grawlix in an article for the National Cartoonist Society.
He formalized this definition in the release of a 1980 text called The Lexicon of Comicana. This semi-satirical and mostly-illustrated glossary of cartooning terms was intended as something of a frivolous project but has actually become a classic exploration of the form. In it, Walker defines the grawlix as actually just one of a number of “maledicta.”
According to an article in Co.Design, “The maladicta is made up of jarns, quimps, nittles, and grawlixes. What's the difference? Quimps are mostly astrological symbols, jarns are usually different types of spirals, nittles are bursting stars, and grawlixes are squiggly lines that represent ‘ostensibly obliterated epithets.' Naturally, they can all be mixed and matched according to the level of profanity a cartoonist wants: Stubbing your toe and dropping an anvil on your foot would result in some very different combinations.”
Of the various maledicta that Walker identified, the term grawlix seems to have emerged as the most evocative catch-all for all others. (Although I guess it's hard to say really. I hear ‘grawlix” about as much in day-to-day conversation as jarn or quimp.)
But it seems true enough. Wiktionary offers Walker's definition first, calling a grawlix “A spiral-shaped graphic used to indicate swearing in comic strips.” However, its second definition says that a grawlix may be considered “typographical symbols, especially '@#$%&!', used (especially in comic strips) to represent an obscenity or swearword.”
And if you consider the way John expresses disdain for Garfield every time the cat shame-gorges on lasagna, or the way Cathy melts down every single time she tries on a bathing suit, or what happens whenever Charlie Brown's friends exclude him for being kind of a downer, the evolution of grawlixes becomes pretty clear.
The grawlix is the comic world's wink and nudge to the reader, the cartoonist's way of saying that which can't be said, the illustrator's elegant solution to the problem of censorship, and the best way to get kids to imagine up their own $#%&*@# swear words instead of taking the same old profanities at face value.