Which beauty/cosmetics company used the tagline "Only her hairdresser knows for sure"?

Clairol’s ground-breaking “Does She… Or Doesn’t She?” campaign, launched in 1956, altered popular perceptions of women’s beauty products.

Shirley Polykoff was the only female copywriter at the Foote, Cone & Belding advertising agency in New York in 1956 when the company began working on a new campaign for Clairol. At the time there was a tendency among ad agencies to view female copywriters as the key to selling feminine products, with many believing that women copywriters better understood the mysterious feminine mind. Her bosses decided to give Shirley a crack at it.

Polykoff, who lightened her own hair, recalled the time her boyfriend (later her husband) had taken her to dinner at his parents' home. His mother had pulled her son aside to ask (essentially) "Does she… Or doesn't she? (color her hair)”. Back then, hair dye was seen as the province of actresses and models, and few other women would admit to it. Polykoff used the encounter to create the "Does She… Or Doesn't She?" tagline.

The campaign featured full page magazine ads picturing close-up photographs of wholesome women, sometimes along with their children, accompanied by the headline “Does she… or doesn’t she?” and followed by “Hair Color So Natural, Only Her Hairdresser Knows For Sure”.

The 15-year campaign was one of the smash hits of mid-century American advertising, and helped encourage women to think of hair color as a fashion choice, rather than a mark of moral standing.