On my iPad, how can I tell if a website is secure on Safari?
If the site is being accessed over HTTPS, then the lock icon is shown (in black).

If the HTTPS certificate has been verified, the lock icon is shown in green.



Both are secure, however the latter vouches for the authenticity of the site as well as the security of the connection.

For example: 


https://www.icloud.com/ shows a green lock icon, having been verified as Apple Inc.


https://georgegarside.com/blog/ shows a black lock icon. Even though it's secure over HTTPS, it hasn't been verified.




You can visit the two links on your iPad to see the difference in lock icon.