Intellectual Property? Copyright? Or just a lot of LOVE?

I was rather proud of the art I designed for a t-shirt this summer. It's cool but of course it's a direct ripoff, um, no, I mean, it was inspired by a well known piece. If I show you my design, below:

You will immediately see the resemblance. You might say, oh that was on a postage stamp:

Or you might say, oh, that was a New York City thing. But you would be remembering wrong:

Actually, the stamp was based on an design and sculpture by Robert Indiana. Yes, it was a sculpture first:

But you can see another copy of the same sculpture in New York City. I saw it just a few days ago:

Actually I didn't take that picture, because if you see it on foot, there is always a line of kids waiting to pose for pictures with it.

Anyway, you can see that my idea for a T-Shirt design was clever but hardly original. I admit to having some guilt about appropriating the design, but also I have been keenly attuned to see who else and where else folks might have borrowed the design.

In Chicago, I saw this:

On TV I saw this:

In a promotional email from the Institute of Contemporary art I saw this:

So, what do you say? How badly did I infringe the copyright of Robert Indiana? Will I be asked to take it down (and destroy the 16 one-of-a-kind t-shirts.) And will I win the case in court, because, "everyone else is copying it"?