Interesting, so using the Break instead, my current acceptance test case seems to interrupt correctly in many cases although I get wild exit codes some times.
However, trying just a simple test, this still does not work. For instance I have 2 scripts running in parallel, using one to attempt to send the signal to the other:
WaitForCtrlC.pl:

use strict;
use warnings;

$SIG{INT} = sub {print "got ctrl-C in waitforctrlc\n"; exit 1;};
print "\nmy pid is $$\n";

while (1) {
   print "waiting for ctrl-C\n";
   sleep 2
}
# should never get here
print "made it past ctrl-C\n";
exit 0;
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And then send the signal to the pid with SendCtrlC.pl:

use strict;
use warnings;

while (1) {
   print "Enter pid to signal:";
   my $pid = <STDIN>;
   chomp $pid;
   print "\nSending signal to $pid:...";
   kill 21, $pid;
   print "\n";
}
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