Safe is the normal behaviour, as documented at the link you quoted. PERL_SIGNALS is a mean of restoring the old, unsafe behaviour.

Also, when I do a perl -V on 5.8.8, the environment variable PERL_HOME is display. Is that used at all for anything?

It seems that perl -V displays all env vars starting with PERL.

$ PERLfoo=bar perl -V
Summary of my perl5 (revision 5 version 8 subversion 8) configuration:
...
  %ENV:
    PERL5LIB="/home/eric/lib/perl5"
    PERLfoo="bar"
  @INC:
...
[download]

There's no implication that the variable is used at all by perl. And since it's not listed in perlrun, it probably isn't.