The rowing men's four team have tweeted a picture of heading in to the Olympic village Post Office to pick up some of the stamps with their faces on.
There are also traditionally sized versions available.
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Through the day, most of the cloud should break up to leave fine conditions for many with spells of sunshine.
The Eiffel Tower in Paris was plunged into darkness, with the Burj Khalifa in Dubia emblazoned with the Union Jack.
The major party leaders' campaigns for the General Election will remain suspended on Wednesday following the Manchester terror attack.