One of my hobbies I enjoy the most is visiting yard sales. I usually go every weekend. I've even had a few myself. At least I had the decency to remove all my signs after the sale.
Most signs just have "yard sale" and an arrow. At the price of gas these days, you sellers should at least have the courtesy to remove your signs. I've been on a lot of goose chases lately.
At the very least, put days and times so we don't waste ours. Not to mention, they cluster up the neighborhood.