Hi Ian and Priti,
The laws to curb illogical horn blowing by cars do exist for the night times – we are also banned to use any kind of horn in the places around residential complexes. But it is extremely tough to keep a check on it. First thing is who will keep the check? Blowing a horn is such a random thing and so wide spread that it can barely be predicted if someone will honk. Even if someone does honk, it is just for a moment, so that person can easily escape due to lack of any proof.
Moreover, honking is basically an act carried out by a number of random people. A crowd has no one face to it, and so it is almost impossible to say that one particular someone responsible.
There are laws which exist for type of horns which can be used. Each car is allowed to come with a certain kind of horn only, and they cannot change or upgrade it. So this keeps the nuisance controlled from a different angle up to certain point. But there is also a secondary car market, which easily allows you to replace the original horns with bigger horns and louder ones too, without any check or pre-requisite. So that beats the whole purpose again.