Trustmarks are images or logos that you can place on your website, to show that you have passed various security and privacy tests. They reassure customers that it is safe to buy from you.
Get your website validated by groups that represent a well known level of security to your customers, like VeriSign, TRUSTe or the Google Trusted Stores program. Display their logos prominently on your website.
Other Trustmarks can include logos of the major credit cards and other payment methods you accept, and logos of the brands you sell.