SSL Configuration for Multisite

Currently, the SSL configuration (using Verisign) for our Multisite sets off untrusted warnings for subdomains.

Is there a way to assign http(s) to only the designated pages that require a secured layer?

As a point of reference, when you visit Apple's website, you can browse both the main site and "store" without the SSL present--when you go to "checkout" is when you see the SSL (see sample links below).

The question: how do we execute the same setup/configuration as Apple.com and prevent the SSL from setting off untrusted warnings for subdomains?

As always, your guidance is highly appreciated.

gist

Reference Links:
http://www.apple.com/
http://store.apple.com/us
https://buyiphone1.apple.com