I have a condo that's for sale or rent, whichever comes first. As you know you can't hang anything on the door nor put a for sale/rent sign out front. So in order to get the word out I'll be giving away flyers to all the little kiddies and their parents who come by for candy. It's a great way to spread via word of mouth!
Take two pieces of cardboard. One for sale, with the price and one for rent, with the price. Attach these and hang them around your neck, so that they always notice them. Boom! You're killing two birds with one stone!