This artwork is from; Uncle T and the Uppity Spy, page Page 20, its a lithograph print and unframed but signed by the artist, image size 16″ x 20″
Sometimes messages were sent secretly, in the words of a particular song. If a slave were to sing “Steal Away to Jesus” for instance, other slaves would hear it, and know there was going to be a secret meeting in the woods that night. Certain songs warned of approaching danger; other songs meant it was safe to move forward. Many whites enjoyed hearing slaves sing, and they would not be suspicious of a black woman like Harriet Tubman singing the day or night away. Tubman also used slave songs to relay other messages.
For example, sometimes she had to leave a group she was leading north to get food or other needed items. She would tell them to hide and wait for her signal. If she came back and sang one song two times, they would know it was safe to come out of hiding. But if there was danger — slavecatchers in the area, for example — she would sing another song. This would mean that the group had to stay in hiding until Tubman sang the “all clear” song. However, if you didn’t know the signal, you might think that Tubman was singing just to pass the time of day.