How can I tell if I'm viewing a secure page in Safari (6.0.2)?
On HTTPS pages Safari shows a small padlock. 

 (screen made with Safari 6.0.2) 

You can see this a little easier in these larger snaps - one of a site where the SSL certificate was not trusted implicitly (signed or otherwise trusted by your Mac) and another where the certificate was valid and signed up the chain by the Mac and shown in green.