From Monday's Foreign Policy:
Rousseff’s supporters have tried to paint the protesters as coming from a small segment of wealthy Brazilians resentful of the PT’s redistributive economic policies. But the size of Sunday’s demonstrations, and the fact that her center-right opponent won 48 percent of the vote in last year’s runoff, show that the conservative force may not be easy to write off.
Protesters chanted against Rousseff and the PT’s left-wing policies, raising comparisons with Venezuela, Argentina, and Cuba. In Rio they held signs that read, “Against the Bolivarian dictatorship,” referring to the colonial-era revolutionary figure held dear by Latin America’s left, and waved placards calling for “Less Marx, more Mises,” citing the late Austrian economist Ludwig von Mises, whose work is influential in libertarian circles.
I guess someone thought, "who's the opposite of Marx?" And he or she (correctly) came up with "Mises." Or it could have been the work of Helio Beltrao.