Glad you asked. If you sign up before August 30, you’ll receive a fancy Per Square Mile t-shirt in addition to the regular member extras. You’ll also have my gratitude for supporting this site (which costs a pretty penny just to host, not to mention the time I spend writing and producing it.)
Only two weeks remain in the drive. After that you can still sign up and receive the member extras, but you’ll be missing out on one sweet shirt. You know you want one.