Square, the mobile payments company, has signed a lease for its new headquarters in the Mid-Market neighborhood of San Francisco, a block away from Twitter. The company moved into its first office back in December 2009, when it had just 10 employees. Now Square has more than 400 employees and plans to have 1,000 people on board by the end of 2013, according to the company. Last month, Square hit it big with $200 million in funding and a deal with Starbucks. The company is processing $8 billion on an annualized basis. Its new headquarters will have an open, collaborative space; a roof deck; a chef’s kitchen; and other amenities for its employees. (Square, GigaOM)