You surely would like to know whether the server which you intend to access via a secure connection actually is the one that it claims to be. However, there are unfortunately technologies around by now that undermine the purpose of an HTTPS connection (see the article on digital fingerprints on grc.com). Here a proxy impersonates the server which you want to access by reading all data of the original certificate and then creating a new one with exactly these data to present it to your browser. Since it is possible to forge any certificate with an appropriate root certificate, the deception cannot be noticed at first glance, however, closer scrutiny gives away the game.
It is here where the digital fingerprints of certificates come into play to enable you to determine whether or not someone is a man in the middle between the destination server and you. If so, the fingerprint of the forged certificate is going to differ from the one of the original. In order to check this, you can instruct this server to fetch the fingerprint of the original server certificate.
Since this server has direct access to the Internet, the result won't be distorted. You can then be sure that the fingerprint being displayed is authentic.
You can obtain the fingerprint of the certificate presented to your browser as follows:
If there is a match, your browser has been presented the original certificate. However, if there's a discrepancy, that's enough reason to be suspicious and you should immediately stop what you intended to do on the encrypted connection.