It can be done a variety of diffent ways in illustrator or gimp..... some designers can use frees vectors and brushes an come up with something incredible while others cant... just play around in Ai Ps Or gimp and youll comme up with something the obey shirts ae some of the siplest designs but s fairley is one hell of a designer and makes the colors and the whole designs just incredible he started with s simple photcopied picture and grew from there.... do you and youll come out with a desing you like dont go for something already out there .... godd luck bro.