G'day Gavin,
I can't see any insecure content on that page, but in Google Chrome there is a warning about the SSL certificate.
It seems that your SSL certificate was signed with an old and untrusted cryptographic method, SHA1. Google Chrome is saying that it doesn't really trust it, and in a future version of Chrome it will actually show a big nasty warning page instead of loading the website. Firefox will follow soon too, and I'd assume also the other browsers at some point.
Here's some details about this:
http://serverfault.com/a/663103/220532
You need to speak to your certificate issuer about getting a new certificate that meets the new browser requirements.
cheers,
Ross
