Well so far they're been paying to all the signature holders regulary, can't called it scam in that regard, until they stop paying that is.
<Bangs head against wall>
All scams pay out,
until they don't.
Madoff paid out for decades, until he didn't.
This
is a scam. It cannot be anything else, it is simply impossible to provide the returns claimed here.
By your definition, on December 9th 2008 Madoff was running a perfectly legitimate investment fund.
In fact, many people had correctly concluded it was a scam, but were ignored:
Concerns about Madoff's business surfaced as early as 1999, when financial analyst Harry Markopolos informed the SEC that he believed it was legally and mathematically impossible to achieve the gains Madoff claimed to deliver. According to Markopolos, he knew within five minutes that Madoff's numbers did not add up, and it took four hours of failed attempts to replicate them to conclude that Madoff was a fraud. He was ignored by the Boston SEC in 2000 and 2001, as well as by Meaghan Cheung at the New York SEC in 2005 and 2007 when he presented further evidence. He has since published a book, No One Would Listen, about the frustrating efforts he and his team made over a ten-year period to alert the government, the industry, and the press about the Madoff fraud.
Although Madoff's wealth management business ultimately grew into a multi-billion-dollar operation, none of the major derivatives firms traded with him because they did not believe his numbers were real. None of the major Wall Street firms invested with him either, and several high-ranking executives at those firms suspected he was not legitimate.