1) Humor.
2) All members must bring a non-member (membership drive).
3) The restaurant will serve anyone.

I believe this is a joke, unless they mean that there is another subset besides members and nonmembers.

I think it might be the following...
1)Anyone is accepted as stated before... Members OR nonmembers.
2)No one is accepted... Members AND nonmembers. (The person has to be both at the same time)

The only problem with the first one is it is using disjunction rather than conjunction ( 'or' rather than 'and' ), which the original statement does not use. However, Nameless' answer 2 makes sense that you have to have two different people one being a member and one being a nonmember.

So, what do you guys think?
1)No one is accepted... Members AND nonmembers.
2)A member has to bring a nonmember

Here's what I got:

1) There are two groups called "members" and "nonmembers", however these titles do not necessarily refer to membership in itself, they are only meaningless names
2) "Members and nonmembers only" would make sense if there was an implicit addendum: "No organisers or managers allowed"
3) nameless - if the restaurant would serve anyone, then it wouldn't be "exclusive" as stated in the OP

What if 'member', is a symbolical referance to the phallical, digit of a male, therefore encouraging females, who would be non members while rejecting those who would seem to be unsure of themselves while either possessing or not, that which would identify them as either.

This is a linguistic problem.

It's joke guys playing on the words MEMBERS ONLY. in that anyone is welcome.

William