Here is what I have on Windows 7. 
```ruby 
irb(main):001:0> Signal.list
=> {"EXIT"=>0, "INT"=>2, "ILL"=>4, "ABRT"=>22, "FPE"=>8, "KILL"=>9, "SEGV"=>11, "TERM"=>15}
```

On OS X 10.7.5
```ruby 
1.9.3p194 :001 > Signal.list
 => {"EXIT"=>0, "HUP"=>1, "INT"=>2, "QUIT"=>3, "ILL"=>4, "TRAP"=>5, "IOT"=>6, "ABRT"=>6, "EMT"=>7, "FPE"=>8, "KILL"=>9, "BUS"=>10, "SEGV"=>11, "SYS"=>12, "PIPE"=>13, "ALRM"=>14, "TERM"=>15, "URG"=>16, "STOP"=>17, "TSTP"=>18, "CONT"=>19, "CHLD"=>20, "CLD"=>20, "TTIN"=>21, "TTOU"=>22, "IO"=>23, "XCPU"=>24, "XFSZ"=>25, "VTALRM"=>26, "PROF"=>27, "WINCH"=>28, "USR1"=>30, "USR2"=>31, "INFO"=>29} 
```

I'm not a big fan of inspecting the `RUBY_PLATFORM` either but I'm not sure how to use `Signal.list` to identify the correct graceful termination signal for the current platform. I'll look for another clear cut way to identify the current platform.