Site seals are not required to be displayed on the secured site, but they do let the user know what type of authority the certificate was signed with.  GeoTrust site seals are dynamic while the RapidSSL seal is simply a static image.  Here are installation instructions for both GeoTrust and RapidSSL certificates:

 

GEOTRUST:

http://www.geotrust.com/support/quick-ssl-support/true-site-seal/

 

RAPIDSSL:

http://www.rapidssl.com/ssl-certificate-support/ssl-site-seal/rapidssl.htm