Aged Metal
Create a new 250 x188 @ 72 dpi graphic and type the letter 'O' in 225 point Arial Black.
Create a new layer and fill it in with white. Filter>Render>Difference Clouds. Add contrast to the image: Image>Adjust>Auto Levels. Hold down the control key and click on the Text Layer, then invert your selection: Select>Inverse and push delete.
Add noise to the image: Filter>Noise>Add Noise, and use an Amount of 10, with Gaussian Blur and Monochromatic.
The next step is subtle. Create a new layer, hold down the control key and click on the text layer to get the selection. Fill that selection with white. Filter>Noise>Add Noise Use an Amount of 250, Gaussian and Monochromatic. Keeping the selection active, add some blur: Filter>Blur>Gaussian Blur and use an Amount of 2. Deselect everything. Change the layer mode of that layer to Color Burn, and change the opacity to 25%.
Create a new layer, hold down the control key and click on the text layer to get the selection. Take a bright orange color (#FFCC00), and use the airbrush tool at a low setting (5%) and color in some of the areas. Change the layer mode of this layer from Normal to Color Burn.
Create a new layer, hold down the control key and click on the text layer to get the selection. Take a bright orange color (#CCCCFF), and use the airbrush tool at a low setting (5%) and color in some of the areas. Change the layer mode of this layer from Normal to Overlay.
Add some depth to the letter: Layer>Layer Styles>Drop Shadow and use these settings: Mode: Multiply; Opacity: 100%; Angle: 120; Distance: 3; Spread: 0; Size: 5.