First open up a new file with contents on "White",for size i usually use size 365x135 pixels, just like in this tut.
Now that u have ur file opened go to Filter -> Render -> Clouds, and press ctrl + c untill it isn't too dark, but not too light either:

Now select a grunge brush pack, for this i will be using a pack called "stalemateisgod" which can be found at deviantart.com.
Before u start to brush make sure u have Mode: Normal and Opacity and Flow at 100% at top of the screen. Now make a new layer by going to Layer -> New -> Layer... (or click CTRL + Shift + N)
Now start brushing, but dont make it too dark yet, brush about 5-7 layers or so, all with a different brush, the Layers window should look like this:

The sig itself will propably be all black, but that's totally normal. Now change all the layers mode to "Soft light" like this:

After that it maybe turn a bit lighter, maybe not. Now u need to change ur forground color to white by pressing either "X" or this little button shown in the pic:

Now brush the top layer (Layer 7 in this case) all white. If it still looks too dark u can brush on the other layers aswell untill it looks good. This is how my sig looks so far:

Now we need to add a render, im going to use this one (u can use it aswell if u like):

Open the pic in PS, and move it on ur signature with the Move Tool (V)
This is how mine looks now:

Now lets blend the pic in a little, by taking a grunge brush and setting the Opacity to 60% and Flow to 50%. After that brush on the sides of the render gently a few times.
Now we need to colorize it by going to Layer -> New adjustment layer -> Color balance.
Now choose a color u want by moving the blocks in the Midtones section. In the Highlights, put -50 in the third box where it says Color Levels:
Now go to Layer -> New adjustment layer -> Brightness/Contrast.
I will be using these settings:
Brightness: 10
Contrast: 30
Next thing we need to do is add the text. Take the text tool (press "T") after that choose a desired font from the top of the window, i will be using Arial Black for this one. Before u type ur text make sure u have the "aa" on Smooth at top of the window. The font size can be changed from the box on the left of that. I will be using 40. Now click on the sig and type ur text. After that move the text layer under the Color balance and Brightness/Contrast layer in the layers window if it isn't already.
Now lets make the text look a bit better. Go to Layers -> Layer Style -> Blending options.
Click on Drop Shadow, and change the Opacity to 50% from 75%. Do the same in the Inner Shadow, and Inner Glow. Now click on Bevel & Emboss, and leave everything else on default except the Size, Change that to 0. Select Gradient Overlay, leave that to default. Now select Stroke, and change the size there to 1, and click the red box and change that to black color.
Now click OK.
Starting to look like a grunge sig right? If it doesn't u may have done something wrong, or then i have

.
Now the last thing we need to do is add a border, by making a new layer on top of all other layers, and clicking ctrl + a to select the canvas. And after that going to Edit -> Stroke.
Width: 1 px
Color: Black
Location: Inside
Mode: Normal
Opacity: 100%
Preserve Transparency: Not selected
Now u only need to save it anymore, by going to File -> Save As... and then selecting JPEG, JPG Format and a name.
And then u are done! I hope i didn't make it too hard to follow, tried to make it as detailed as possible. And sorry if theres any typo's.
If u have some problems with the tutorial, please post here and i'll try to help u out.
This is how mine looks:

Have Fun!
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