Normal Service

For the last couple of weeks the car has been displaying "Service Required" and showing me a little green picture of a spanner. I figured it was trying to tell me something. I checked in the handbook and apparently it needs servicing. So today I took it to my favourite garage and turned them loose on it. I've got it back and the car seems just the same, although the message has gone and I am a couple of hundred pounds poorer.

Questions abound. What would happen if I'd ignored the message?Would the spanner turn red?  If I kept ignoring it, would the text change to "Service Me Now or Die" and the airbag go off? Would the engine management system eventually start making the car run badly and force my hand? Would the GPS, if I had one, tell me that all roads lead to the garage? Did the service just involve turning the message off?