This indicates an attack attempt against a Command Injection vulnerability in Logsign.
The vulnerability is due to insufficient sanitizing of user supplied inputs in the application while handling crafted HTTP requests. A remote attacker can exploit this to execute arbitrary commands, via a crafted HTTP request.
Logsign version 4.4.2 and version 4.4.137
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor