I still have to hear-of, read-of, etc. these infamous court cases. (Example: I've never heard of someone being sentenced for not locking his car, having it stolen and used to kill a pedestrian.)
Maybe in some countries the approach is to sue for anything, in others (mainly continental europe) a more pragmatic approach applies. For this reason, the simple fact of naming the network "forSensibleUseOnly" should be more than sufficient.
But comming back to the thread issue, using a password would not provide information on whether someon is "stealing" wireless internet.