Buy Happiness, Buy A Bike
Illustration by Anthony Oram, available for purchase here.
More prints by Anthony Oram available here.
Related

Image (and idea) by Anthony Oram, on Twitter.
In "Images"

Some designs found through sources on Twitter, many others from this awesome post by Melody Stone with a selection of tee designs.
In "Images"

Illustration by Anthony Oram, shared on Twitter.
In "Images"