MEXICO CITY — Armando Ruiz and Verónica Villafuerte held each other tight, cuddling, caressing, stretched out on a bench in the middle of a busy promenade here. Nearby, just past a couple deep kissing in the grass, a man toyed with the buttons of his paramour’s blouse.

Children played all around. Cars passed. No one cared.

“It’s a little more open now,” Mr. Ruiz said after sitting up. “We can enjoy ourselves.”

In Havana or Rio de Janeiro, well, big deal. But historically this has been a city of formalities, of long-sleeved shirts, not skin-tight skirts. Blushing has generally been the response to overt sexuality, along with a lexicon of double entendres to mask X-rated desires with banal words, like “coger” (which, officially speaking, means to grab).

And yet, despite such reserve — or perhaps because of it — public affection has increasingly become a symbol of what experts describe as a city learning to loosen up. Government officials here now boast about having some of Latin America’s most liberal laws on abortion and same-sex marriage. Meanwhile, sex shops can now be found in even the fanciest neighborhoods; oh, and this month, Mexico City played host to a five-day sex entertainment show that drew 120,000 fans — placing it among the biggest sex fairs in the world.