When Jean Valjean finally gets out of jail, he's handed a yellow ticket. Woohoo! Ticket to freedom!
Or not. It's more like a ticket to even more misery. That's because the Yellow Ticket is a symbol of social rejection. Jean Valjean is required to carry it with him at all times in order to show people that he is an ex-convict, or else he'll be in violation of his parole and go back to jail. The problem is that this ticket makes people turn him away wherever he goes. As Valjean says to Bishop Myriel, "This is my ticket-of-leave – yellow, as you see. That's why everybody turns me away" (188.8.131.52).
Talk about massively unfair. All he did was steal a loaf of bread to feed his starving family, and he got thrown in jail for nineteen years because of it. Now that he's served his time and is out, the so-called free world seems to be worse than jail—because at least he could sleep and eat in jail. Thanks to that yellow ticket, Valjean sadly finds out "the meaning of liberty when it is accompanied by a yellow ticket" (184.108.40.206), which is not really liberty at all.
The yellow ticket symbolizes the terrible way society treats its outcasts. It shows us that "freedom" doesn't mean a whole lot if what it means is that you're free to starve and die. The thing to remember here is that, while Valjean has a literal yellow ticket, all of the book's outcasts have some sort of "yellow ticket" that keeps them outcast. It could be as obvious as an illegitimate child or as invisible as a pair of miscreant parents, but either way, the world will eventually find it out—and then kick you out to starve and die on the streets.
No wonder people are rising up in the streets.