The work, which started earlier this month, should see the sign restored to its bright white glory before Christmas.
The sign, which is on top of Mount Lee in the Hollywood Hills north of Los Angeles is managed by the Hollywood Sign Trust and has been regularly repainted - but not as thoroughly as it is being done this time.
"This is the most extensive refurbishing effort of its kind in nearly 35 years for the sign, which will be repainted in its signature white.
"By protecting and preserving this towering treasure that is the sign, the trust helps strengthen its symbolic role as the beacon of the entertainment industry," the trust said.
The original sign had been erected in 1923 to advertise a property development called Hollywoodland, but the last four letters were removed in the 1940s. The sign then fell into disrepair until it was restored in the 1970s after a campaign that saw nine donors shell out 27,777 dollars to "adopt" one letter each.
Recently it was threatened again, when investors who own land surrounding the giant letters indicated plans to sell the plot to developers.
But Playboy mogul Hugh Hefner helped secure the sign in 2010, along with the then-California governor Arnold Schwarzenegger.