Geometrically frustrated antiferromagnets RBa(Co/Fe)4O7 (R=rare earth or Y) exhibit a weak ferromagnetic component in the high-temperature spin-liquid phase. Based on a symmetry approach, we recently proposed a possible explanation of this phenomenon. Due to the polar nature of their crystal structure, a coupling between time-odd scalar spin chirality which we suggest as the primary order parameter and macroscopic magnetization is possible as follows from the general form of the appropriate free-energy invariant. Thus, these materials are unique model systems exhibiting a mysterious chiral spin-liquid state which we propose to study via muon spin-relaxation measurements.