It's not a command line switch. "--" marks the end of the command line switches. That's the case for just about every unix tool.

$ ls -l *
ls: invalid option -- -
Try `ls --help' for more information.

$ ls -l -- *
-rw------- 1 eric users 0 2009-11-18 14:08 -a-
[download]

Another trick is to provide an equivalent path that doesn't start with "-":

$ ls -l ./-a-
-rw------- 1 eric users 0 2009-11-18 14:08 ./-a-
[download]

And finally,

$ rm -- -a-

$
[download]

Since it's not a command line switch, it's completely ignored by Perl.