Interesting dilemma Veerendra.
I like the response from "bus2perf".
However, someone needs to take responsibility for saying that there is a concern with lack of productivity. Ideally this would come from a Manager. Unless the concern is expressed openly (and this doesn't mean targeting particular individuals) there will continue to be no motivation to change no matter how many programs you put in place.
I would be inclined to at least consider addressing staff at a staff meeting and saying something like "I've often noticed that there is a high level of conversation in the office and I'm not sure how much of this is work related. I've also noticed visitors to our area paying attention to this and wonder what kind of impression it creates".
Even if staff are not prepared to acknowledge the problem at least it is in the open and you can follow up with dropping into non work related activities to observe what is going on. Even if you say nothing further, many will get the message.
Who knows, it might even be a problem to other staff who feel they just have to put up with it. I know that I often feel a bit cross when others interrupt my day with very long chats about their personal lives or other non work related matters.
Good luck with it, but as "bus2perf" writes, think about whose responsibility this is and how you engage them in a change process. It is about workplace culture and that cannot be effectively changed with a heavy hand.
Progress Enterprise
<link outdated-removed>