The Dialtone Pickups team were looking for a simple, single colour T-shirt design that not only used their logo, bud did so in a way that let people know what their company was about. What better way to let people know you create awesome guitar pickups than by putting your logo in a guitar (right where a pickup would go).
I often use AppSumo to get great deals on graphic and development software. Now you can get $10 (after your first purchase) when you sign up at AppSumo too. Full disclosure, I also get $10.