To be honest, Tk is not very good at accessing the window manager's statusbar, but Gtk2 is. The example below, is a Tk program, which you can place wherever you want as an indicator. For Gtk2, see Gtk2::StatusIcon Demo ( which may not work on all WindowManagers :-( )

#!/usr/bin/perl
use Tk;
use strict;

my $mw = MainWindow->new;
$mw->geometry('20x20-20-20');
$mw->overrideredirect(1);

# make right mouse button click an exit
$mw->bind( '<3>' => sub{ exit  } );

my @color = qw/red lightgray/;
my $bits = pack("b8"x8,
"...11...",
"..1111..",
".111111.",
"11111111",
"11111111",
".111111.",
"..1111..",
"...11...",);

$mw->DefineBitmap('indicator' => 8,8, $bits);

my $label = $mw->Label(-bitmap=>'indicator', -fg=>'red', -bg => 'black
+')
   ->pack( -fill=>'both', -expand=>1);

$mw->repeat(500,sub{$label->configure(
                               -fg=>$color[0]);
                               @color=reverse(@color);
 });

MainLoop;
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