The instant online symbol of global support for Paris after last week’s attacks was a roughly rendered peace symbol with an Eiffel Tower in the middle of it.

The French designer Jean Jullien sketched it as soon as he heard the news of the atrocity. He called it “Peace for Paris,” and it immediately became a sensation on social media.

Its success is a sign of the times.

We have become experts at treacly online mourning. We take grotesque atrocities and launder them into trite symbols and slogans that are usually self-congratulatory and, of course, wholly ineffectual.

The 19th-century author William Dean Howells once said, “Yes, what the American public wants is a tragedy with a happy ending.”

On social media, the happy ending is the widely shared and tweeted image or hashtag.

After the slaughter at the offices of the satirical French magazine Charlie Hedbo earlier this year, it was “Je suis Charlie,” or “I am Charlie.”

It was a well-intentioned expression of solidarity, so long as you overlooked the absurd presumption of it.

You are Charlie? Oh, OK. Then draw a sketch of Muhammad and post it online. Better yet, do it over and over again, until you get constant threats and your office is firebombed, just as a warm-up.

No, you aren’t Charlie. (For that matter, Charlie isn’t even Charlie anymore — it’s given up on mocking Islam for understandable safety reasons.)

Last year, when the Nigerian terrorist group Boko Haram kidnapped 200 schoolgirls, Twitter exploded with the hashtag #BringBackOurGirls. First lady Michelle Obama held up a sign with the phrase on it. If Boko Haram was shamed by its Twitter feed, it showed no signs of it. The only girls who were brought back escaped on their own. The Nigerian military has rescued other girls, armed with weapons considerably more powerful than a hashtag.

The “Peace for Paris” image is simple and emotive, if inapt. The peace symbol sprang out of the nuclear disarmament movement in the 1950s and gained wider currency in the protests against the Vietnam War.

It still carries a strong whiff of its original purpose of hectoring the West for its alleged militarism and, as such, is off-key as a reaction to a barbarous assault on helpless civilians in a peaceful city.

Paris doesn’t need to give peace a chance. It doesn’t need to make love, not war. It doesn’t need to be more understanding or more hopeful. It needs to be better protected by all those unsentimental means that have been neglected in recent years, or overwhelmed by the growing threat of ISIS.

Paris — and more broadly, France and the West — needs more surveillance of suspected terrorists and police raids; a more restrictive immigration policy that doesn’t create large, unassimilated Muslim populations, or welcome terrorists as refugees; and a serious, multi-layered campaign to destroy ISIS and deny it the safe havens from which it recruits, trains and plots against the West.

If someone can come up with a catchy symbol for that, I’ll embrace it. (Although “La Marseillaise” isn’t so bad: “To arms citizens/Form your battalions/March, march.”)

Meanwhile, spare me the #PrayforParis hashtag. Forgive me if I’m unmoved by lighting world landmarks up in red, white and blue, or your putting a tricolor filter on your Facebook profile picture. And please don’t tell me, in the words of the designer Jean Jullien, that “in all this horror there’s something positive that people are coming together in a sense of unity and peace.”

Nothing positive comes from innocents getting shot down in cold blood for the offense of going to a concert on a Friday night. It there aren’t going to be more — and worse — attacks in our cities, the path ahead won’t be one of unity and peace. It will be the hard, thankless work of protecting civilization from its enemies.