There's a fun custom that began around the time the new (then NW) terminal opened at DTW. Passengers sign or write messages on the stones or rocks (I think they'd be considered small river rocks) in the planters holding ornamental trees in the terminal. If you look around the big circular fountain under the central train station and DL SC, near an information desk as the top of the escalators going down to the psychodelic tunnel to the B/C gates for RJs, you will find that most of the rocks have writing and sometimes interesting pictures, cartoons, or graphics. Some people have inscribed rocks with their FT handles or (now defunct) NW WorldPerks account numbers. At some point during the NW/DL merger, most of the decorated rocks disappeared because, in the words of a SC agent, some people wrote inappropriate things. Now, however, we seem to be back to a state in which most of the rocks are decorated once more. It's good to plan ahead by bringing a felt tip pen (or several in different colors) because ball point pens don't work. (Perhaps someday Gargoyle can be induced to carve a rock for the project.) You might want to subtly remove a rock you like that's blank, take it off somewhere to decorate it (the cublcles in the SC are good for this purpose) and then again subtly return it to a position you like as you walk past on the way to your gate. Have fun. I did one before the big removal (mine was not at all inappropriate, but I haven't seen it recently) and a second one more recently.