I have only been out to GOM once but I must say that the number of locations is mind-boggling by NS standards, so I can see where helonorth and SASless are coming from.
he1iaviator mentions AIS and I must say that I am somewhat surprised that this is not already the goto system for destination ID. Sure, there are problems with AIS data being corrupted or not updated occasionally but surely you just put in the contract that the rig should have up-to-date AIS.