I have found some interesting information on the sybolism of the egg.
Did you know, for example, that...
"Breaking the smaller end of the egg betokens only disappointment of one's hopes — with that supposedly lying in store, it makes sense to smack it open at the larger end. The discovery of a double yolk within is cause for terror or celebration depending on which school of thought is followed — some say it presages a wedding, others a death. " link
and some more:
"Eggs that have no yolk were considered to be very unlucky as they are traditionally believed to be laid by the cockerel, whilst an egg with a double-yolk was said to indicate an imminent death in the family. Sailors were also advised not to mention the egg by name but by the term 'roundabout' to avoid misfortune at sea. Poking a hole by accident in the bottom of the shell after eating a hard-boiled egg though is considered to be very lucky, but never throw the shell on a fire or the hen will never lay again and a storm may brew at sea. The Scots (UK) believe that crushing the shell is the best way to avoid any negative events happening. The Scots also believed that witches would collect up any shells left whole and use them to sail out to sea in order to sink the ships. This belief is thought to stem back to Roman times. The Japanese traditionally thought it also unlucky for a woman to step over an eggshell as this would cause her to become confused and agitated to a state of what was called madness
And more Germany-specific trivia:
" In Germany, in 1918, for example, eggs were so difficult to find after World War I that to buy one it was necessary to have a doctor's prescription."
A lot of sources list eggs as a symbol of fertility, so perhaps a double yolk symbolizes mega fertility.