Retrieve the assignment logs after your signal, like this:

token.signal();
LoggingInstance loggingInstance = token.getProcessInstance().getLoggingInstance();
List assignmentLogs = loggingInstance.getLogs(TaskAssignLog.class);
Iterator iter = assignmentLogs.iterator();
while (iter.hasNext()) {
 TaskAssignLog taskAssignLog = (TaskAssignLog) iter.next();
 TaskInstance taskInstance = taskAssignLog.getTaskInstance();
 // [...]
}