As I explained yesterday, the Freedom Bell was paid for with donations from regular Americans who wanted to show their support for West Berliners. Much of the money was raised by school children who also collected signatures from people across the country under the guise of the Crusade for Freedom. You can read more about the Freedom Bell and see pictures of it being hoisted into place here.
The millions of American signatures collected during the Crusade now reside in this specially created room. The sign above reads, "Here lie the signatures of millions of American citizens that have signed to show their support for freedom."