what other "signals" can be utilized in perl

These are the signal names recognized by Perl:

$ perl -V:sig_name
sig_name='ZERO HUP INT QUIT ILL TRAP ABRT BUS FPE KILL USR1 SEGV USR2 PIPE ALRM TERM STKFLT CHLD CONT STOP TSTP TTIN TTOU URG XCPU XFSZ VTALRM PROF WINCH IO PWR SYS NUM32 NUM33 RTMIN NUM35 NUM36 NUM37 NUM38 NUM39 NUM40 NUM41 NUM42 NUM43 NUM44 NUM45 NUM46 NUM4 NUM48 NUM49 NUM50 NUM51 NUM52 NUM53 NUM54 NUM55 NUM56 NUM57 NUM58 NUM59 NUM60 NUM61 NUM62 NUM63 RTMAX IOT CLD POLL UNUSED ';

The above list can also be obtained from Config.pm's $Config{sig_name}.

There's also the two pseudo signals, __WARN__ and __DIE__.

and what keys activate them?

The following signals are often sent in response to terminal input:

• SIGINT
• SIGQUIT is a more "serious" version of SIGINT that provides a core dump.
• SIGTSTP sends a process to the background.
• SIGSTOP is an uncatchable signal that freezes the process.
• SIGCONT resumes a process frozen by SIGSTOP.

You can see to what key these are bound using the following:

$ stty -a | perl -ne'
   $b{$1}=$2 while /\b(intr|quit|susp|stop|start)\s*=\s*([^\s;]+)/g;
   END {
      print "SIGINT:  $b{intr}\n";
      print "SIGQUIT: $b{quit}\n";
      print "SIGTSTP: $b{susp}\n";
      print "SIGSTOP: $b{stop}\n";
      print "SIGCONT: $b{start}\n";
   }
'
SIGINT:  ^C
SIGQUIT: ^\
SIGTSTP: ^Z
SIGSTOP: ^S
SIGCONT: ^Q

Most signals aren't sent as a result of terminal input. The following a commonly used signals and what normally causes them to be sent:

• SIGSEGV is sent when the program does an illegal operation (often the result of using a bad pointer).
• SIGHUP is sent when the session's terminal disconnects.
• SIGTERM is sent to request that a process exits.
• SIGKILL can't be caught. It's sent to forcibly terminate a process.
• SIGCHLD is sent when a child exits.
• SIGALRM is sent by alarm.
• SIGPIPE is sent when writing a pipe with a closed read end.