Article: In January 1989, Madonna signed an endorsement deal with soft-drink manufacturer, Pepsi. In one of her Pepsi commercials, she debuted her song "Like a Prayer". The corresponding music video featured many Catholic symbols such as stigmata and cross burning, and a dream of making love to a saint, leading the Vatican to condemn the video. Religious groups sought to ban the commercial and boycott Pepsi products. Pepsi revoked the commercial and canceled her sponsorship contract. The song was included on Madonna's fourth studio album, Like a Prayer, which was co-written and co-produced by Patrick Leonard and Stephen Bray. Madonna received positive feedback for the album, with Rolling Stone writing that it was "as close to art as pop music gets". Like a Prayer peaked at number one on the Billboard 200 and sold 15 million copies worldwide, with 4 million copies sold in the U.S. alone. Six singles were released from the album, including "Like a Prayer", which reached number one, and "Express Yourself" and "Cherish", both peaking at number two. By the end of the 1980s, Madonna was named as the "Artist of the Decade" by MTV, Billboard and Musician magazine.

Now answer this question: When did Madonna sign an endorsement deal with Pepsi?
January 1989