Olfactory cues are especially important for nocturnal mammals such as bats and can communicate an individual's condition and facilitate mate choice. Here, we introduce a novel odorous substance found on the forearm of reproductive male fringe-lipped bats (Trachops cirrhosus), which we term “forearm crust.” We continuously captured bats over a 3-year period to determine the prevalence and possible seasonal distribution of this forearm crust. We evaluated males to elucidate whether forearm crust was associated with specific morphological characteristics. Males with forearm crust were captured throughout the year, but we found an increase in captures of males with a forearm crust from September to December, prior to peak female pregnancy in March. All males with a forearm crust had enlarged chest glands and testes. Males with a forearm crust had significantly higher body condition indices than males without a forearm crust. We observed males in their natural roosts and in captivity, and describe a novel stereotyped behavior in which males scratch the body dorsally and ventrally, insert a claw into their mouth, and then lick their forearm repeatedly. Males with a forearm crust licked their forearm significantly more than males without a forearm crust. Together, these data suggest that this novel odorous forearm crust is a male reproductive trait. Further investigation is needed to understand its role in reproduction.