SysMLv1: CAUTION: Only a Signal can be used for a SendSignalAction or MessageEvent trigger of an AcceptEventAction, not a Block or ValueType, even if they are valid types for a SysML FlowProperty! But you can "wrap" a Block or ValueType in a Signal.
SendSignalAction::signal: The Signal whose instance is transmitted to the target. Source Unified Modeling Language 2.5.1
