Both need to be very eye-catching - striking images catch people's attention and draw them in. Keep wording to a minimum - less is more - so that the words are large enough to be read. Choose a size that is going to fit your venue - small letter-size is not ideal if you are trying to target passing vehicular traffic. Also think about durability if they are for a long term project. Signs also needs to be clean and clear especially if they are going to be viewed from a distance.