Police are hoping to crack the case of a third egg stolen from a city-wide exhibition in the build-up to the Olympics.
Cartoonist Charlie Anson designed the 2ft tall "Our Team" fibreglass egg, which was taken from its plinth outside the National Gallery in Trafalgar Square, London, on Thursday night.
The Olympic-themed egg is one of 210 in the Faberge Big Egg Hunt, the world's biggest ever Easter egg hunt, which will raise money for the Elephant Family and Action for Children charities.
Two similar eggs that were stolen in February were safely returned within days.
Thirty of the Olympic icons were sold at a Sotheby's auction on 20 March and Anson's Our Team egg is one of 180 available to buy online as part of a final target of £2m for the charities, including the money raised at the auction.
Anson is best known for painting satirical cartoons for the cover of the London freesheet City AM.
A spokeswoman for both charities said: "It is so sad that on the day that the British Olympic kit is unveiled, Charlie's 'Our Team' egg - a real tribute to the Games - is stolen.
"In the true Olympic spirit of camaraderie and togetherness, we appeal to whoever took the egg to return it so it can continue to make London proud and help raise vital funds for two charities who have worked so hard to put this on.
"All the eggs are due to be displayed in Covent Garden from 3 April, and it just won't be the same without our 'Our Team' egg.
"We are so appreciative of everyone's support and the hunt, the fun and the fundraising goes on, so please do get out there and enjoy it this weekend."
The eggs have been decorated by some of the world's leading artists, architects, jewellers and designers including Mulberry, Sir Ridley Scott, Zandra Rhodes, Diane Von Furstenberg, Marc Quinn, Bruce Oldfield, the Chapman Brothers, Theo Fennell, William Curley, Candy and Candy, Zaha Hadid, Bompas and Parr and Polly Morgan.
Anyone with information about the egg should contact 020 3124 0661 or can return the egg to 10 Great Queen Street, London WC2B 5GG.