Everytime time media need an image about the Hunger Games, they use this golden bird
What is the significance of this bird?
This bird is the Mockingjay, a famous symbol used especially in later on books, but first mentioned in the first book. Basically, it's a pin that was worn by Katniss during the Hunger Games.
The Mockingjay resulted from a genetic mishap where the Capitol genetically engineered blue jays to exactly reproduce conversations, known as jabberjays, during the first revolution against the Capitol. Their usefulness eventually waned, as the revolutionaries found out about them, and started passing false intelligence to the birds. These birds weren't suppose to mate, they were all male, but they ended up mating with native mockingbirds, to produce mocking-jays. The mockingjays had some voice - in particular, they could sing simple songs - but did not have the full range of reproduction of the jabberjays. The Capitol ended up with egg on their faces, as not only did the jabberjays prove a resounding failure, but the reminder of that failure lives on long after all the pure jabberjays died off.
There is considerable more to this symbol from future books, which I will list with spoiler tags.
As it is a bird, it is commonly symbolic about freedom. Katniss wants to get free from the capitol. As we can see, the bird is flying on an arrow- Katniss is going to be free by fighting :)