One good way to distinguish my company from the others is with the recognition of our logo, which is a predominant part of our identity. Just getting a postcard in front of our clients on a regular basis keeps our firm's identity in their minds, even if they don't read the sales message itself. Postcards do have some limitations, such as having only a small area on which to print. A single postcard really isn't the way to introduce all aspects of your firm to a prospective client. There isn't enough space on the postcard for the amount of information that should, more appropriately, be part of a larger mailing package.
Postcards are also best when used as a two-part sales strategy.
That is, you'll rarely get an appraisal order from your postcard mailing directly but it can elicit interest in your appraisal firm, which can result in an order at a later time. Your postcards will be most effective if you design your sales message to entice the recipient to call or write for more information. You can do additional selling and provide the prospect with a full packet of materials once they've responded to the postcard. Let's say you want to promote your firm's ability to provide appraisals for PMI removal. You wouldn't want to design a postcard explaining the whole program and asking for an order.