Chapter 15 Unified Threat Management for FortiOS 5.0 : Custom Application & IPS Signatures : Custom signature keywords
  
Custom signature keywords
Information keywords
attack_id
Syntax: --attack_id <id_int>;
Description:
Use this optional value to identify the signature. It cannot be the same value as any other custom rules. If an attack ID is not specified, the FortiGate automatically assigns an attack ID to the signature. If you are using VDOMs, custom signatures appear only in the VDOM in which you create them. You can use the same attack ID for signatures in different VDOMs.
An attack ID you assign must be between 1000 and 9999.
Example: --attack_id 1234;