Help me find something like this?

So I was at this festival last weekend, and there was a guy there wearing a white tshirt with a screen printed pattern on th front of it. And he got this light out of his pocket and drew on the pattern on his shirt with this light pen, and the shirt held all the little scribbles he drew temporarily. It was in a blacklit room, so it was neon. It was awesome, and I wish I could find one. Can anybody help me?