Humans are able to communicate in sophisticated ways with only sparse signals, especially when cooperating. Two parallel theoretical perspectives on cooperative communication emphasize pragmatic reasoning and joint utility mechanisms to help solve ambiguity. For the current study, we collected behavioral data which tested how humans select ambiguous signals in a cooperative grid world task. The results provide support for a joint utility reasoning mechanism. We then compared human strategies to predictions from Rational Speech Acts (RSA), an established model of language pragmatics.