text: To mark the poster launch Natalie Bennett, the party leader for England and Wales, met up with parliamentary candidate Caroline Lucas in Brighton.
  Ms Bennett warned voters "the time for half measures is over" and urged people to "vote for what you believe in".
  She said a Green vote would ensure big firms and rich individuals would pay their "fair share".
  Ms Lucas, who became the UK's first Green MP when she was elected in 2010, added: "We have a bold message that will resonate with the people of Brighton and Hove, and across the country.
  "Only the Green Party is willing to stand up to the establishment parties on issues like climate change, a resilient economy and protecting the NHS."
  The Green Party has vowed to put up the top rate of tax to 60p in the pound, which Ms Bennett said would bring in an extra £2bn a year for public services while acting as a disincentive to firms paying "excessively high salaries".
  She added that her party wanted to call for a review of all "commercial animal racing", saying there were animal protection issues which needed to be addressed.
  Main pledges
  Policy guide: Where the parties stand
  "We should be spending our money on public services that meet our essential needs, we should be spending our money on building council homes, homes for social rent.
  "We need to invest in renewable energy, energy conservation, there is a whole range of things we need to do to make British society fit for the 21st century," she said.
  The Greens have also proposed a "wealth tax" which would be 2% a year levied on people with assets of more than £3m which, Ms Bennett has claimed, could bring in £25bn a year "by the end of the Parliament".
  Later, Brian May, the lead guitarist of the rock band Queen, is expected to join Ms Lucas in Brighton to talk about democracy and the importance of voting.
  A full list of candidates for Brighton Pavilion can be found here.
  Subscribe to the BBC Election 2015 newsletter to get a round-up of the day's campaign news sent to your inbox every weekday afternoon.
target: The Green Party has launched a national billboard campaign urging people to "vote big, vote brave".