Here is a little routine i came up with for making black and white, dirty, grungy looking text.
It works best with thin, sans serif fonts that look handwritten.
Canvas Size 640x400px. Font is Segoe Print 215px.
Apply G'MIC → Degredations → Noise [spread]:
Apply G'MIC → Deformations → Textured Glass
(The most important slider here is 'Edge attenuation'. Dont make it too ripped, but also not too smooth)
This gives you the basic irregular grungy outline.
To add more texture, create a new black layer on top of your text.
Go to Filters → Noise → RGB-Noise. Put all channels to the max and uncheck 'Independent RGB' to get b/w noise.
Set layer mode to 'Screen' so the black becomes invisible.
To make the Noise more blotchy go to G'MIC → Repair → Recursive Median
Then go to 'Hue/Lightness/Saturation' and take the Lightness all the way down.
Sometimes its necessary to apply the filter a second time, with a Lightness decrease of about -35.
Then merge down.
In some case it might be necessary to sharpen the text (Unsharp Mask).
For example you can put the 'Amount' to the max and then play with the 'Threshold'.
To finalise the image i applied RGB Noise to the whole canvas, with all sliders set to 0,08. This gives the background a bit of dirt as well.