I watched a video by Cherry Hill, something like "100 Horsekeeping Ideas" or something like that.
She suggested hanging a lanyard with a toy attached from the spigot. Every time you turn on the water, you put the lanyard around your neck. When you turn it off, you return it. If you forget and walk off with the thing around your neck, you will at some point (or someone else will) wonder why you have that dumb toy on you!
Works great, by the way!
Now I want to watch that video again...