A. Simple Grunge Signature (Novice, skill level 0/10)
Start by making a new picture (Cntrl + N) and using these settings:
Next go to Fliter > Render > Clouds ( Thank you Qweasd )
Press Cntrl + U and check colorize to change the color of the Clouds. Change it to your liking and place your render on your picture.
Next make a new layer (f7 to open layers tab) and start adding in Grunge brushes. For each brush make sure you have a new layer. You can also go back (Cntrl + U) and change the clouds color to something more appropriate.
Once you're done, you can change the opacity and fill of each of the layers.
Other finishes i got using different brushes:
