Are reviewers supposed to know each others' identity, after the reviewing process is finished? I reviewed an article and submitted my review along with a short letter to the editor. As a service the journal permits to see the decision letter and the other review. However, I am also able to see the other reviewers' letter to the editor, which is signed with a name. My own short letter to the editor I did not sign with my name.

Is this supposed to be? If not, should I do anything in particular if I do find out by accident?

The issue is somewhat addressed in some of the answers for the question Are reviewers allowed to discuss their review with each other?. One answer states you're not meant to find out, while another one states once you've submitted your own review, it is normal to know who the other reviewers are and be able to see their reviews. There are two different issues here:


Knowing the other reviewers' identity during the reviewing process.
Knowing the other reviewers' identity after the reviewing process.


Is case (2) normal?

Edit: I might add that the policy of the journal is not a double-blind: the full list of authors and affiliations of the manuscript were purposefully disclosed to the reviewers.
No, its not normal to know who the other reviewers are if the journal has a double-blind review policy ( my background is Engineering disciplines, might be different in other fields). 

What I have experienced in the double-blind review process both as a reviewer and the author:


Knowing the other reviewers' identity during the reviewing process? NO, not normal.
Knowing the other reviewers' identity after the reviewing process? NO, not normal.
Knowing whether the editor accepted or reject the paper? NO (a very good practice as I have learned).