Such a simple thing, but a little hand painted stone (painted by you of course!) could be such a gift from the heart and costs next to nothing! (nothing if you already have a bit of acrylic paint and a brush)
I'll tell you right now, this was on my list of things to create since last year. An outdoor chalkboard for the kiddos. We don't have much sidewalk and we live on a busy street, so I'm not too fond of my kids using chalk that close to the cars. This is right up my alley.