Steps:
1. Make your sig,banner or whatever.
2. Create a new layer,Then select
3. Then create a box the size that you want your bar to be like(don't deselect your box until you have filled it with color) Like this
4. Fill your box with the color that you want using the brush tool,Like this(now deselect the box)
5. Right click your bar layer and set the blending settings to around this
6. Ok nearly there! Now open image ready by clicking this
7. Select your bar layer by left clicking it,Now with the image moving tool (arrow) move your bar to the left of your image like this
8. Now click on your first slide with your bar set the the left and then click the duplicate button like this
9. Now you should have two slides,Now select your second slide and move your bar to the far right of the image like this
10. Ok now you should have 2 slides,One with your bar to the left and one with your bar to the right,Now select your first frame and click the tween button.The button looks like this
.
11. When you click the tween button you should get a menu come up,Use these settings!(click ok)
12. Now select your last frame and click tween again and then use the same settings but change "tween with" to first frame.
13. Click play and your bar should go back and forth across you image.
After your done it should look something like this.








More Photoshop: