Nostalgia is a brand of men and women's cosmetics created by Veidt Enterprises.
Advertisements for the perfume appear throughout the events of Watchmen and characters are seen to use it, like Sally Jupiter, Laurie Juspeczyk and Dan Dreiberg. Rorschach snatches an aftershave bottle from Dreiberg's house and applies it to his face; the bottle is broken during the skirmish outside Edgar Jacobi's house and a cop comments that "he stinks". On Mars, as Laurie is emptying her bag, she hurls her bottle which crashes on Dr. Manhattan's clockwork palace, causing it to shatter and collapse.
According to Veidt, the success of the range is down to the romantic atmosphere and soft focus of the ad campaign. The marketing strategy capitalized on the public anxiety during the Cold War, and conveyed an idyllic idea of a modified, half-remembered past when everything was safe.
Veidt predicted (and anticipated) that the public worries and uncertainty about the shadowy future would not last forever, so the marketing philosophy that aimed to withdrawal in nostalgy would eventually be obsoleted.
He proposed to phase out the Nostalgia line by '86 to make way for a new brand for a different target group. This brand, called Millennium, will feature more controversial imagery to reflect a futuristic utopian vision. The new line would be ready in the summer of 1986. Posters for this new brand can be seen on the last pages of Chapter XII.
Nostalgia is representative of the characters' reminiscences, memories and flashbacks. This is particularly notable in Chapter IX. In the end of Chapter XII, the shift of focus to the new Millennium brand represents a larger change in the characters, looking less towards the past and more towards the future.
It's made obvious that Veidt used the brand and marketing of Nostalgia as a manner to make people long about an idyllic past and be uncertain about a shadowy future. More certainly, the contrast between Nostalgia and the later Millennium, would make the buying market conform more effectively to his new utopia after the threat of the nuclear war.
DC Universe Rebirth
Following Watchmen's integration into the DC Universe, a character known as Mr. Oz (heavily implied to be Ozymandias) is shown to be covertly monitoring the current Superman. An agent operating on behalf of Mr. Oz bears a tattoo on her forearm, a circle with a Z running through it, heavily resembling the Nostalgia logo.