A few years ago some DISers were trying to figure out a way to identify other random DIS board members at the parks. It was decided that Lime Green would be a great color because at that time it was very rare to see. People would tie lime green ribbons to their bags or make tags or wear a lime green t-shirt in hopes of seeing other DISers in the parks and saying Hi.
Then Home Depot began carrying the Disney paint and the swatches were in the shape of Mickey heads. The color Alien Green is the "unofficial" color for the DISboards and people began using those as an easy way to make tags for their fanny packs, backpacks, lanyards, shirt pins, window decorations and just about anything you can imagine. Usually we write our username on it or other sayings--my kids wear ones that say "future DISer" on them. And of course, these days lime green is a hot color so you can't just assume that anyone with a lg t-shirt or hat or bag is a DIS member. So the LGMH sets us apart.
When you see someone with that on their bag or stroller or person then you know they are a DISer and want to meet others so conversations ensue. Sometimes just a "Hi" sometimes a short conversation or more. One of the first DISers I met this way, in the food court at All Star Movies, I am still friends with and in fact she came all the way out by me on a family vacation with a priority of us going out for dinner.
Now I can' promise you that your HD won't object to you taking them. I don't ask and I don't take ALL of them. I generally just walk by and take a few anytime I am in. I have other colors also that I have used. But I also have repainted and needed the paint swatches so I don't feel to bad about it! Generally we don't ask, we just take a few (you want extras for your bags in case you lose them or mess one up). If you don't want to use those you can also just cut out Mickey heads in lime green from craft foam ( much more durable), or construction/scrapbook paper, or any other material. There are some patterns floating around here on the DIS. You might check in the Creative DISigns board found near the bottom of the main forums list.