Simplify the following text for a Grade 9 native English-speaking person.
Original: The graphic was popularized in the early 1970s by Philadelphia brothers Bernard and Murray Spain , who seized upon it in September 1970 in a campaign to sell novelty items .
Simplified: The design was made popular in the early 1970s by a pair of brothers , Murray and Bernard Spain , who though of a great plan to sell novelty items .