There are two issues here: NM concealed carry statute which prohibits carrying in an establishment which sells liquor, and the Trespass statute.
The Trespass statutes indicate specifics for signage: found at http://nxt.ella.net/NXT/gateway.dll?f=templates$fn=default.htm$vid=nm:all
30-14-1.1. Types of trespass; injury to realty; civil damages. (1983)
A. Any person who enters and remains on the lands of another after having been requested to leave is guilty of a misdemeanor.
B. Any person who enters upon the lands of another when such lands are posted against trespass at every roadway or apparent way of access is guilty of a misdemeanor.
C. Any person who drives a vehicle upon the lands of another except through a roadway or other apparent way of access, when such lands are fenced in any manner, is guilty of a misdemeanor.
30-14-6. No trespassing notice; sign contents; posting; requirement; prescribing a penalty for wrongful posting of public lands. (1979)
A. The owner, lessee or person lawfully in possession of real property in New Mexico, except property owned by the state or federal government, desiring to prevent trespass or entry onto the real property shall post notices parallel to and along the exterior boundaries of the property to be posted, at each roadway or other way of access in conspicuous places, and if the property is not fenced, such notices shall be posted every five hundred feet along the exterior boundaries of such land.
B. The notices posted shall prohibit all persons from trespassing or entering upon the property, without permission of the owner, lessee, person in lawful possession or his agent. The notices shall:
(1) be printed legibly in English;
(2) be at least one hundred forty-four square inches in size;
(3) contain the name and address of the person under whose authority the property is posted or the name and address of the person who is authorized to grant permission to enter the property;
(4) be placed at each roadway or apparent way of access onto the property, in addition to the posting of the boundaries; and
(5) where applicable, state any specific prohibition that the posting is directed against, such as "no trespassing," "no hunting," "no fishing," "no digging" or any other specific prohibition.
C. Any person who posts public lands contrary to state or federal law or regualtion [regulation] is guilty of a petty misdemeanor.
The uniform jury instructions indicate that the person prosecuted knew, or should have known, that he was trespassing to be found guilty. An implication is that the "I found a door without a sign" is not likely an effective defense. I doubt there is yet a trial to detemine whether a sign that substantially meets the legal requirement is sufficient (I'm thinking of the "should have known" clause in the jury instruction).
I thought I recalled that armed trespass is a more serious offense in NM, but I can't find any such reference today.
It might be worth asking the manager of the motel in question whether he was attempting to comply with the concealed carry requirement, or if he intended to ban weapons throughout the establishment. If the former, a little education is appropriate.
It is my understanding that presence of a bar is not intended to prohibit entry to the entire building under NM CC law, although this may not be specifically spelled out in current law. Your motel room is an extension of your home in NM, I believe, just like your car, so possession of a weapon could not be banned there, I suppose. Again, probably never tested in court.
I hope this clears things up a bit.
DISCLAIMER: I AM NOT A LAWYER AND THE ABOVE IS NOT LEGAL ADVICE: IT IS MY PERSONAL OPINION ON THE SUBJECT.
C