For me, it was the Museum of Science and Industry in Chicago, Il. It was all about getting to be up close and personal with the science, especially the body slices! Science is so much more fun when it's interactive. I've never left science since...
while signs didn't stand out in particular i do remember distinctly learning about the idea of "rules" and the way they define a social context. and when i first saw a command line, i couldn't help but think it was a pretty strange way to order things around, which led to a prolonged interest in interface design/how our societies are affected by our command of technology (or its command of us). hacking, for me, is the ability manipulate that relationship or at least be curious as to how it manipulates me. what's your story? how'd you first think about hacking?