Signature definition in Computer Security terms:
The ability to trace the origin of the data.
Source(s): NIST SP 800-113
A recognizable, distinguishing pattern associated with an attack, such as a binary string in a virus or a particular set of keystrokes used to gain unauthorized access to a system.
Source(s): NIST SP 800-61 Rev. 2
A pattern that corresponds to a known threat.
Source(s): NIST SP 800-94
A set of characteristics of known malware instances that can be used to identify known malware and some new variants of known malware.
Source(s): NIST SP 800-83 Rev. 1
reference: CSRC Glossary