SSL Blog readers will know that I believe the presence of the VeriSign Secured Seal causes site visitors to be more likely to complete transactions. The idea appeals to my reason. Extensive research indicates that consumers are afraid of online security and that they opt out of transactions in response. The VeriSign Secured Seal is widely recognized as an indicator of premium security on a site. Therefore it follows that site visitors will be less reluctant to proceed when the VeriSign Secured Seal is present.
It's also supported by anecdotal evidence. I can't count the number of people who have told me that they like to see the seal on a site before they put in confidential information. Nor the number of site owners who have told me that they believe their own customers expect to see the seal and reward them for including it.
However, in terms of hard measured results, I have only had a single data point to go...