If you 1ook too contented and complacent, the bar staff may assume you are already being served. They do not like people to keep others waiting while they make up their minds. They don't like people standing idly against the bar when there are a lot of customers wanting for service. But they do, and if you follow these tips you should be able to do so, too. The correct behaviour is to offer them a drink.
Pubs pride themselves on their egalitarian atmosphere.
A tip in cash would be a reminder of their service role, whereas the offer of a drink is a friendly gesture.