Xiu Xiu are inviting their audience to be part of the band. There's three ways of getting involved, but this is the most interesting:
For the aurally inclined, visit Xiu Xiu's merch table, ask for the "tape recorder", and record a short audio fragment (text, music, etc.). Drummer Ches Smith will then write short percussion pieces incorporating the sounds recorded at every stop. After the tour, the pieces will be available at the Xiu Xiu blog as free mp3s, credited to each town.
You can also join in by asking nosey questions or by sending disposable cameras to the band for them to fill with pictures.