Considering that communication between neighboring agents may be cooperative or antagonistic, this study is concerned with the bipartite time-varying output formation tracking (BTVOFT) problem for heterogeneous multi-agent systems (MASs) with multiple leaders on signed digraph. A fully distributed event-triggered output feedback formation tracking (FDETOFFT) control scheme is constructed to address this problem. It is noteworthy that the control scheme does not involve any global information, which enables it to be implemented in a fully distributed fashion. The biggest contribution of this study is to extend event-triggered techniques to the formation tracking control scheme. Compared with previous related works, continuous communication between neighboring agents is avoided. Moreover, it is further proved that no agents exhibit the Zeno behavior.