Pre-registration of Studies 1 and 2: https://osf.io/txbku. Pre-registration of Study 3: https://osf.io/ef857. Pre-registration of Study 4: https://osf.io/mxt7a. A reliable assortment of committed individuals is crucial for success in intergroup conflict due to the danger of shirking. Theory predicts that reliable communication of commitment is afforded by costly signals that track cooperative intent. Across four pre-registered studies (total N = 1,440, general US population), we used the public goods game where groups competed for resources to investigate whether and how costly signals function to assort cooperators. We found that costly signals assorted more cooperative participants, creating groups that would win most of the between-group clashes. The same effects were not observed when participants were assigned to signal, implying that signaling tracks but does not create cooperative intent. However, contrary to costly signaling theory, we found that low cost signals were more effective in cooperator assortment compared to high cost signals and suggest that future studies need to focus on signaler perception of cost/benefit trade-off of signaling.