Just a simple sign that you carry in your back-pack. At any point you can hold it above your head while you stand still, or you can plant it in the ground, and stand close to it. The text would be from a limited list such as "sauces for sale", "wanted: no-no powder", "fancy a chat?" or a range of random/funny sayings. As soon as you move off a held placard drops back into your pack. Walking more than a few steps away from a planted sign also makes it pop back into your bag.