Title refers to the number of votes that separated the two Presidential candidates in the election of 2000 between George W. Bush and Al Gore in the state of Florida, which granted Bush the Presidency.
When the television networks called Florida for Gore at 7:38, the heavily republican panhandle was open for voting till 9:00. In March of 2001, the New York Times said that that cost Bush 8,000-12,000 votes. The reliance on VPN by the networks caused the controversy of the 2000 election.
By coincidence, 537 is one less than the total number of votes in the Electoral College that elects the President.