Giz - good suggestion.  You are right, that a FWB allows you to always get the right polarity if you don't know your source. That is not actually the problem here. The 12V trigger is ALWAYS ground on the ring and +12 (or 0V when off) on the tip. The problem is once I added the diode you have to actually make sure you wire up the jack correctly. Before I added the snubber the circuit had nothing you had to pay attention to as far as polarity goes making it more idiot proof.

But if anyone is really worried, take Giz's suggestion and use four 1N4148 diodes in a full wave bridge. This will not only make the circuit no longer polarity sensitive, but the bridge provides inductive snubbing (although at -1.4 volts rather than -0.7).