Sorry, forgot to mention explicitly that this only works starting with Perl 5.10.0 — AFAIK, older versions only ever provide the signal name (I get the same output as you with 5.8.8).

Update: FWIW, this is the respective code snippet from mg.c (line 2854) in the Perl 5.10.0 sources:

#if defined(HAS_SIGACTION) && defined(SA_SIGINFO)
    {
     struct sigaction oact;

     if (sigaction(sig, 0, &oact) == 0 && oact.sa_flags & SA_SIGINFO) 
+{
          if (sip) {
           HV *sih = newHV();
           SV *rv  = newRV_noinc((SV*)sih);
           /* The siginfo fields signo, code, errno, pid, uid,
            * addr, status, and band are defined by POSIX/SUSv3. */
           (void)hv_stores(sih, "signo", newSViv(sip->si_signo));
           (void)hv_stores(sih, "code", newSViv(sip->si_code));
#if 0 /* XXX TODO: Configure scan for the existence of these, but even
+ that does not help if the SA_SIGINFO is not implemented according to
+ the spec. */
           hv_stores(sih, "errno",      newSViv(sip->si_errno));
           hv_stores(sih, "status",     newSViv(sip->si_status));
           hv_stores(sih, "uid",        newSViv(sip->si_uid));
           hv_stores(sih, "pid",        newSViv(sip->si_pid));
           hv_stores(sih, "addr",       newSVuv(PTR2UV(sip->si_addr)))
+;
           hv_stores(sih, "band",       newSViv(sip->si_band));
#endif
           EXTEND(SP, 2);
           PUSHs((SV*)rv);
           PUSHs(newSVpvn((char *)sip, sizeof(*sip)));
          }

     }
    }
#endif
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I can't find any entry in the Changes file when this has been added, but it's definitely not there in 5.8.8.   (Note the "#if 0 /* XXX TODO:...", btw, which wraps the "pid" code.)