MONTPELIER — Capitol Grounds is planning a new campaign to market its coffee brands, using the Green Mountain State’s signature 802 area code. It is another branding move that has marked the ascent of the popular Capital City café since it opened on State Street in 1998. Its location in two different buildings over the years has become a favorite of many as a place to pause, sip coffee, eat lunch, peruse work by local artists and purchase coffee by the pound. As the popularity of the café has grown, so has demand for products that include its coffees, T-shirts, hats and mugs, which will also embrace the 802 Coffee campaign. Its most recent offering, Bernie’s Beans, has been a runaway success, with packages of coffee featuring the Vermont senator’s unmistakable visage.