In "The Odyssey", what sign does Zeus send to assembly, and what is its meaning? How did Penelope hold off the suitors?

In Book 20 Zeus sends a bird omen, an eagle clutching a trembling dove, as the suitors plot the death of Telemachus, and Amphinomous warns the others to give up the plot. In Book 21 just as Odysseus, disguised as the beggar, strings the bow, Zeus "cracked the sky with a bolt," terrifying the suitors before Odysseus shoots the arrow through the twelve ax-handles.

Penelope has held off the suitors for three years by a simple trick. She told them she would choose a successor to Odysseus when she had completed weaving a funeral shroud for Laertes, her father-in-law. A shroud is the garment he would be buried in (or cremated, depending on the custom). Every day she would weave some of the fabric on her loom, and the suitors could see her; at night, however, she would unravel part of what she had woven during the day. Her progress, therefore, was slow. The suitors failed to notice this fact because they were busy partying, eating her beef and drinking her wine, abusing her hospitality. When they discover the trick, they are angry and demand she make her choice immediately.