Hmm...It's like going to a club and seeing a sign that says "No Drinking".
Then you go into the club, pull a beer out of your pocket, and drink it. And this is totally acceptable.
Well, that scenario would be up to the club owner's discretion. If when he says "No Drinking" he means "We don't tolerate or allow the use of alcoholic beverages excluding ones brought by the customers", then there's no way around that and people are allowed to bring alcohol inside. But if by "No Drinking" he means "We don't tolerate or allow the use of alcoholic beverages including ones brought by the customers", guess that's it for alcohol in that place.
Are you suggesting that we should be more specific with the "No Items" rule? The details pretty much go without saying, as we can see all players understand the rule and we all have an universally-agreed definition of the rule.