Tutorial
You can show GeoTrust secure images and also secure images from your merchant provider. You would want to contact your Merchant provide to get their secure scripts or graphics.
GeoTrust
Visit GeoTrust and grab the code and paste this into your pages.
http://www.geotrust.com/support/quick-ssl-support/premium-true-site-seal/
Authorize.Net
Login to your control panel:
http://www.authorize.net/solutions/merchantsolutions/onlinemerchantaccount/seal