Non-state actors (NSAs) play an important role in violent conflicts, but unlike state actors they cannot (be forced to) sign international conventions tying their hands. The non- governmental organization Geneva Call has stepped into this void and solicits NSAs to sign and allow monitoring of conventions banning particular activities, for example the use of landmines. We propose a game-theoretic model to assess the motivations for NSAs (and states) to sign such conventions and how they affect conflict behavior on the ground. We find that selection issues are of crucial importance linked to the incentive to signal resolve, both by states and NSAs. Empirical analyses of conflict behavior in countries where Geneva Call has been active support the implications of the theoretical model.