What does 'setting the seal on eight years' mean?
Here's the context:

IN 2010, when Brazilians elected Dilma Rousseff as president, their country seemed at last to be living up to its huge potential. The economy expanded by 7.5% that year, setting the seal on eight years of faster growth and a steep fall in poverty under Luiz Inácio Lula da Silva, Ms Rousseff’s political mentor and the leader of the centre-left Workers’ Party (PT).

Thanks a bunch!
http://www.economist.com/news/leaders/21625780-voters-should-ditch-dilma-rousseff-and-elect-cio-neves-why-brazil-needs-change

Question

What does 'setting the seal on eight years' mean?
Here's the context:

IN 2010, when Brazilians elected Dilma Rousseff as president, their country seemed at last to be living up to its huge potential. The economy expanded by 7.5% that year, setting the seal on eight years of faster growth and a steep fall in poverty under Luiz Inácio Lula da Silva, Ms Rousseff’s political mentor and the leader of the centre-left Workers’ Party (PT).

Thanks a bunch!
http://www.economist.com/news/leaders/21625780-voters-should-ditch-dilma-rousseff-and-elect-cio-neves-why-brazil-needs-change

Answer

Randy had a very good answer...but keep in mind you may never hear that phrase put that way exactly again. I've been here on Earth for quite a few years and can't say that I've heard it. I think I may have heard "putting the seal on..." or "putting the stamp of approval on...". But even though I may never have heard it, I still knew what they were trying to communicate.

Answer

"Setting the seal on eight years of faster growth..." gives the idea that the year served to signify approval and confirmation for those previous years' policies and the progress attained during that time.