In computing, a file signature is data used to identify or verify the content of a file. In particular, it may refer to:
- File magic number: bytes within a file used to identify the format of the file; generally a short sequence of bytes (most are 2-4 bytes long) placed at the beginning of the file; see list of file signatures
- File checksum or more generally the result of an hash function over the file content: data used to verify that the file content integrity, generally against transmission errors or malicious attacks. The signature can be included at the end of the file or in a separate file.