If you followed the instructions, you have installed a kernel source package, named
linux-source-3.13.0, e.g., by
sudo apt-get install linux-source-3.13.0
sudo apt-get install linux-source
which installs a virtual package that installs the versioned package as a dependency.
Having done that, you can find the file you were looking for (using the package name):
dpkg -L linux-source-3.13.0 |grep -F signal.c
and get the pathname(s) of any files in that package named "signal.c"
If the package was actually a tarball of the sources, you would have to extract those files, e.g., using
tar. In that case,
dpkg -L linux-source would only list the tarball (and the grep would return nothing).
For the case of a tarball, you could do this:
tar tvf $(dpkg -L linux-source-3.13.0) |grep -F signal.c
if it contained only one file. But supposing you had something like
then the file you are looking for would be in the "tar.bz2" file, so...
tar tvf $(dpkg -L linux-source-3.13.0|grep -F .tar.bz2) |grep -F signal.c
would show the pathnames within that tarball for "signal.c"