Most companies have a logo to represent themselves with. Just as you would include a logo on your business card or company letterhead, it's important that the logo also be present on your free postcard design. On a related note, if your company has its own website address, you'll definitely want to include that somewhere on the postcard. Many consumers want to learn more about a company without coming under the radar of overzealous sales representatives, so they would prefer the passive approach -- exploring a company's website. Including both a logo and a web address for your company on your postcard design can do wonders for increasing exposure to your company's presence.
Postcard Design