Partisan pranksters struck San Francisco overnight, covering four blocks of signs on the city’s Bush Street with “Obama Street” signs, NBC affiliate KNTV reports. The covers look professional, and chalk messages on the pavement encourage pedestrians to look up and notice the “change.” A rally is planned today at the street’s terminus, marked by a small, but official, “end” sign. It is unclear whether an investigation is under way. (More Barack Obama stories.)