A lot of people think this is a sign over "the Gates of Hell".
It's actually over the City of Dis, which is on the 5th circle of Hell.
Most people misquote it as well. "Abandon hope, all ye who enter here" is the usual one. "Abandon hope, ye who enter here" is another.
It's the use of "all" that seems to confuse people. Under the circumstances you'd think that would be the least of their worries.