The sign is a necessary part of the design. Instead of weakening it, the sign makes the overall design much stronger. The reason the image isn't strong enough to stand on its own is that the content is slightly too obscure without signage.

And while the joke isn't amazingly funny, it has a simple charm to it. I wouldn't say it falls flat just because it doesn't actually make you laugh. The adorable little peas in their cute little helmets make the joke funny enough to warrant a smile.

Also, it's important to remember that it's a shirt design, not a picture as such. On a shirt, sometimes a simple, cute picture with a tiny gag is more effective than a big complicated masterpiece.

I gotta say, I like the shirt.. although the idea wasn't the most original or funny, it was very well executed.

I'm with Amunro, the peas decked out in their little helmets are cute.

Articulate response. I maintain my position, but I'll let it lie. :)