SigNote is a US $0.99 app that lets you add symbols or hand drawn text to any of the photos on your phone. You can grab symbols or graphics from a large on-line library accessed through the app, or you can jot something down on a piece of paper, capture it with your iPhone camera, and layer it on top of your images.
Once you have the graphic, it can be re-sized, moved around or rotated. The app supports up to 7 layers, and you can erase any mistakes you made. Images can be saved back to your photo roll, or emailed or sent to Facebook. Help is built into the app, and there is even a video demonstration.
This is a clever idea for an app. It's not expensive, and provides a clever and easy way to personalize your photos without having to use an external editor like Elements or Photoshop. An update to the app, released today, adds some extra foregrounds and allows the user to adjust the size of the eraser for precise editing. The only improvement I would offer is I'd like you to be able to draw on screen rather than have to find a piece of paper and a marker to create your own graphic.
Check the gallery for some shots of the app in action.