private void initMark() {
        Arrow arrow = new Arrow(Vector3f.UNIT_Z.mult(2f));
        mark = new Geometry("BOOM!", arrow);
        Material mark_mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
        mark_mat.setColor("Color", ColorRGBA.Red);
        mark.setMaterial(mark_mat);
    }
A red arrow to mark the spot being picked.
jme3-examples/src/main/java/jme3test/collision/TestMousePick.java