Modern humans are supposed to have a bulging frontal squama, but little quantitative evidence is available on this topic. Most analyses included the browridge, the rest of the vault, or the whole skull, possibly confounding factors associated with the spatial relationships of the frontal bone with the other cranial elements. After the analyses of the frontal width and of the parietal curve in the human genus, here’s a quantitative approach to the curvature of the frontal squama (Am J Phys Anthropol 2013). Modern humans do actually have a more bulging frontal bone, independently upon orientation or position of the squama. Nonetheless, there is some overlapping between modern and extinct variation, suggesting caution when dealing with single specimens. Early modern humans display the same degree of frontal curvature than living modern humans.
See also this recent paper:
Athreya S. 2013. The frontal bone in the genus Homo: a survey of functional and phylogenetic sources of variation. J. Anthropol. Sci. 90:59-80. [pdf]