As images have EXIF data which provide info about where and how they are created, do any Text Editors append such kind of descriptive details to code files? For example I use Coda for my programming works. Does Coda sign any files created by itself? Is it possible to find out the author of two different projects by just looking at the inners of the files?
EXIF files (as well as JPEG, PNG, and other image formats) contain lots of metadata in addition to images. Text files contain text. If your code is stored as a text file, there's probably nothing in there except your code. Even if you tried to hide data with non-printing characters, there's usually a way to reveal them in most editors.
Many IDEs will store metadata about your code files seperately, usually in XML files (though it could also be done as a binary file) somewhere else. In Eclipse, there's a .metadata directory in your workspace folder that contains XML files which store information about your code (such as when you last synced with source control, any markers in the file for IDE-specific tools, which regions are folded, how far you've scrolled, etc...). Coda might have a similar system, I'm not sure.
As far as "signing" a text file, the closest thing I've ever seen that does this is placing special text in a file, such as
$Author: $ or
$Date: $ and then some other tool will replace these tokens with the appropriate values (usually on check-in) such as
Author: Some Coder. This is still visible as text.
I suppose it would be possible to store code in a binary format (or as an XML file) that merged code and code metadata into a single file. I don't know of any specific systems that do that, but it certainly could be done.