Shane, it tends to be the sites that manipulate the rankings (black hat) know all those tricks and if all it took was a seal from an SSL company, they would have a different one on each page. It would be surprising that the seal actually gives you page rank, it most likely does the opposite since an outbound link only passes juice to the destination and all those seals link directly to the ssl provider.
As Ryan points out contacting Verisign directly will give you some insight, they are a company built on reputation and would not say it adds Google rank when it does not. You have to consider what their product is 'trust' and if they give you false information that hurts their marketting when you discover that is not the case. They would tell you what I said in my first reply, that their seal brings customer conversions, which is ultimately what you are after.
Generally ecommerce sites exclude their ssl pages via robots.txt or nofollows so the question does not get raised. If the content on those pages is secure but not authenticated then the value is limited as it is public and open to exploit. As a developer, I have attended many seminars on this topic alone.
The rank gain you get is secondary (from more tweets, blog links etc because people trust your site and like it) rather than a direct corelation.
Read the paper (relevant section below) from the link:
If I use SSL on my pages, will we be PageRank'd higher then non-ssl pages? So far, there is NO conclusive proof that a SSL site will get higher Google/MSN/Yahoo search rank listing compared to the same site which is unencrypted. In fact there seems to be no positive or negative result if you have your pages encrypted or not. This is because the quality of the data on the site is not validated by SSL, only that the certificate is independently verified. The most important factor in Google's PageRank for example is the amount of high quality sites linking back to your site. The idea being that if a site like Digg or CNN link to your site then your page rank will increase because their page rank is high. This is completely independent of whether your page is encrypted or not.