Beause UTF8 is byte order independent I'm not certain why you want to include a BOM (unless it is simply to have as nearly empty a file as possible with the proper encoding). Having said that, the following will create a file that contains only the UTF8 representation of the byte order mark (\xEF\xBB\xBF). I threw in a newline for good measure, which you can exclude as necessary for your application.

#!/usr/bin/perl

use warnings;
use strict;

open OUTFILE, ">:utf8", "./myutf8file" or die $!; 

print OUTFILE "\xEF\xBB\xBF\n";

close OUTFILE;
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Update:I somehow missed borisz's reply above, which does the same thing. I wish I could claim simultaneous posting, but it looks like his was about 3 hours before mine. :-p