A "footprints in the sand tattoo" refers to a Christian poem in which Jesus is carrying someone who is too weary to walk through the sand. The tattoo can feature footprints, a quote from the poem or other spiritual symbols like a cross.
Some tattoos that are an ode to the "Footprints In the Sand" feature an image of Jesus carrying someone who looks weary and worn on a shore. The most famous quote from the poem is at the end when the person asks Jesus why there are only one set of footprints in the sand. Jesus replies,"the times you see only one set of footprints in the sand were the times I was carrying you." This line is often part of the tattoo as well.