Variation in the linguistic use of handshapes exists across sign languages, but it is unclear how these iconic handshape preferences arise and become conventionalized. In order to understand the factors that shape such handshape preferences in the earliest stages of language emergence, we examined communication within family homesign systems. Homesigners are deaf individuals who have not acquired a signed or spoken language and who innovate unique gesture systems to communicate with hearing friends and family (“communication partners”). We analyzed how characteristics of participants and stimulus items influence handshape preferences and conventionalization. Participants included 11 deaf homesigners, 24 hearing communication partners (CPs), and 8 hearing non-signing adults from Nicaragua. Participants were asked to label items using gestures or signs. The handshape type (Handling, Object, or combined Handling + Object) was then coded. The participants and groups showed variability in iconic handshape preferences. Adult homesigners’ families demonstrated more conventionalization than did child homesigners’ families. Adult homesigners also used a combined Handling+Object form more than other participants. Younger CPs and those with fewer years of experience using a homesign system showed greater conventionalization. Items that elicited a reliable handshape preference were more likely to elicit Handling rather than Object handshapes. These findings suggest that similarity in terms of handshape type varies even within families, including hearing gesturers in the same culture. Although adult homesigners’ families were more conventionalized than child homesigners’ families, full conventionalization of these handshape preferences do not seem to appear reliably within two to three decades of use in a family when only one deaf homesigner uses it as a primary system.