Warning: contains spoilers for Superman: Son of Kal-El #7!
DC's Superman has famously never worn a mask to conceal his face, making him one of the outliers of the genre when compared to the likes of Batman, Spider-Man, etc. But the Superman franchise, as is the case with life in general, changes over time, almost always for the better. In this instance, Superman: Son of Kal-El #7 reveals Superman's first mask - but it's not exactly Superman wearing the disguise.
When Clark Kent left Earth, he passed on the mantle of Superman to his young son Jonathan Kent. Jonathan has inherited all the powers of his father, his general worldview, and his ability to see the capacity for good in all creatures great and small - but lacks his experience. As such, this new Superman is often unsure of himself, even as he easily battles monsters and supervillains on a regular basis. But just like his father, he doesn't wear a mask when he flies into action...until now.
Superman's new boyfriend Jay Nakamura, an intrepid journalist in the same vein as Lois Lane, invites Superman to the floating headquarters of The Truth, Nakamura's organization that seeks to undermine and eventually end the evil President Henry Bendix's vice grip on the island nation of Gamorra. Before boarding the boat, Jay offers Superman a mask to wear. "You think I'll attract less attention if I wear a mask in public?" asks Superman. Jay responds in the negative; he's offering Superman a job at The Truth. But the real truth is exactly what identity the mask is covering up.
While Superman does have a secret identity (at least in the past; he abandoned it to save civilian students from a gunman), his personality is exactly the same as his alter ego. Peter Parker becomes noticeably more confident and prone to clever comebacks and jokes when he puts on the mask of Spider-Man. Meanwhile, Batman sees his cowl as his true identity and Bruce Wayne as the mask. But Superman puts on the mask to hide the fact that he's Superman, not Jonathan Kent - because Superman is his personality. His altruism is no act.
Superman quickly ditches his mask as soon as a creature appears from the ocean floor and flies off to stop it from threatening the city (to no avail; the creature was set upon by henchmen sent from Superman's latest supervillain). Note how he removes his mask while going into battle, not donning it; Superman is as kind, heroic and optimistic as his reputation that proceeds him. Superman's secret identity is, in actuality, not a secret at all, but the honest truth.