The most effective technique for identifying live client systems on a LAN is using ICMP Echo Requests. ICMP Echo Requests, commonly known as 'ping', are used to determine if a host is reachable and responsive. In contrast, TCP FIN scanning is generally used to identify open ports on a system, Traceroute is used to trace the path packets take to a specific destination, and DNS Zone Transfer is used for transferring DNS zone data between servers. Therefore, ICMP Echo Requests are specifically designed for identifying whether a system is live on a network.