Does the padlock at a checkout mean your page is secure?
And if there is no padlock does that mean it's not secure?
Great question. I don't have all the information, but I can tell you that there are different levels of protection. The main thing is that "HTTP" is the protocol, "HTTPS" directs the URL toward the Secure Socket Layer (SSL).
There are several types of SSL, a self-signed certificate (which can be created essentially for free) and certificate an individual or business purchases (more reliable and secure - as well as usually verifiable).
There are different levels of security as well 128-bit encryption, 256-bit encryption (these two are perhaps the most common). However, they do go higher (512-bit, 1024-bit and possibly beyond). The higher the number the better the encryption (and hopefully security)
There is also PCI compliance (or Bank Level Security). There are several visual variations to the lock (there is a "black lock", a "green lock" and entire "green URL bar". These aren't necessarily indicators of more or less security but they levels of perceived security (usually you pay a lot for the entire green URL bar).
The important thing is do you trust the website and does it have the lock? You can usually click on the lock or an "info" icon next to it to get detailed information. You can also set your browser level security to help filter.
As always, if something seems off, leave the site immediately.