Is there much point in putting up notices which can easily (and will) be ignored? If there are rules in places which state people should not be causing a nuisance through excessive noise, what is needed is enforcement of those rules, and for that you need authoritative people. You cannot expect the more considerate members of the public to do this as the selfish/thoughtless individuals have long since worked out they can retaliate against standard members of the public with no comeback. There also have to be consequences to repeated violation of the rules. Without all that, the issue is permanent, and it is apparent now that some have an entitlement attitude (which comes from a lack of consequences to actions) to doing what they want in public shared spaces as though they were at home.