"...Religion is the sign of the oppressed creature, the feeling of a

heartless world..."? What does this quote mean?

"The wretchedness of religion is at once an expression and a protest against real wretchedness. Religion is the sign of the oppressed creature, the feeling of a heartless world, just as it is the spirit of unspiritual conditions. It is the opium of the people.”-Karl Marx
It's not really a misquote, just a typo... My finger pressed the 'n' instead of the 'h', however, I did know it was sigh and not sign... Sorry for the typo.