Start a new document, large enough to place your stamp on. For this tutorial, I am using 250x150.

Now, select RED as your foreground color, and your background color to BLACK

Then use the type tool and type in your text. Use a bold font, I used Arial Black, size 50px.

Now go to Layer->Rasterize->Type - this will convert the vector text to bmp.

Now use the rectangular marquee tool

and make a selection AROUND the text....

Now go to Edit->Stroke

Then you can deselect the selection by pressing CTRL+D

Now apply this filter:
Filter-> Brush Stroke->Spatter.
Spray Radius: 17
Smoothness: 5

Note: These settings can vary.. depending on how washed out you want the stamp to look

Go to Select-> Color range, then use the color picker to select the BLACK from your stamp.

What we've just done is select ALL the black spots on the stamp so we can delete it from our stamp.. creating the stamp effect.

So with the selection selected, hit DELETE .. you can hit delete several times to make sure its all deleted.