Cute concept, but technically speaking, the sketchy lines are difficult to see on the solid shirts (esp the brown/yellow ones) and maybe it is the picture size, but I can't read the sign at all.
Also, size/placement wise, from far away it would just look like two blobs on someones chest. I like that it is asymetrical, but maybe it would look better over a pocket or something.
Keep trying!
=)
NOTE: This is slightly optimized (for the sake of file-size), and as such, the out-of-the-lines look is not as accurate as the original.