In brief , your correct to assume any external resource that is hosted on https:// with any type of SSL/TSL etc will cause no noticeable effect to any of your visitors.
We had this exact same question when we were forced to include some remote JS by our payment card processor.
After some research with every device and browser combination we could get hold of ( and using some web tools such as browsershots.org and modern.ie .
We found all the browsers we tested only reffered to the URL of the page loaded ( and it's headers ) when giving a padlock/secure connection logo to the client/visitor.
It is very common when including external JS/images/ widgets etc, for the included external resource / file to have vastly different cipher chains for TLS / SSL negotiation.
Even expert write-ups our own PCI standards daily scanner and industry expert resources we found like www.ssllabs.com, give you an overview and a grade on your servers ability to negotiate TLS/SSL/SPDY etc, they dont even load the document content, let alone look for any included external resources. They just look at your ability to handshake at the server level.