We rent a house on a small community within a larger urbanization.  We have lived here for 18 months and have cats.  Yesterday signs were put up around the community area saying that cats and dogs are now prohibited; no one has spoken to us or written to us at all.  Is this legal?

Yes it may well be if that is what the community has voted. If you are only renting I don’t think you will get a vote as it is for the owners. I suggest you contact your landlord and ask him as he should have been notified by the community of what has been agreed at their meetings.