From NPR:

The artifacts are stacking up as director Lonnie Bunch gathers material for the Smithsonian National Museum of African American History and Culture. The first national museum to celebrate the legacy of black Americans is scheduled to open on the National Mall in 2015....

...Bunch brings out a yellowed hymn book. On the inside cover, there's the signature of none other than Harriet Tubman, who led slaves on harrowing journeys to their freedom.

"This is one of the great treasures of the museum," he says.

One of the ways Tubman signaled slaves was by singing hymns. "So she'd sing 'Steal Away to Jesus' or 'Swing Low, Sweet Chariot,' and you would know it's time to go. And so to be able to have a hymnal that has those songs in it that was hers is just pretty amazing."

The hymnal came to the museum by way of one of Tubman's last living descendants, who gave it to collector Charles L. Blockson. Bunch and his team traveled to Philadelphia to get it from Blockson. "When he pulled this out," Bunch recalls, "the room went silent and people got ready to cry."

According to Blockson, Tubman didn't learn to write until later in her life, and the signature inside the hymnal is one of her early attempts at signing her name. When he said that, Bunch says, "Well, everybody lost it."

Our God is a god of liberation and justice.  Harriet Tubman knew that we can can still learn from her insight.