What six-character signature identifies a GIF89a file?

The six-character signature that identifies a GIF89a file is **GIF89a**.

It is the file’s six-byte header, written as ASCII characters at the very beginning of the data. In hexadecimal, those bytes are `47 49 46 38 39 61`, which decode to “GIF89a.” File-identification tools use this kind of fixed opening sequence, often called a magic number or file signature, to recognize formats even when a filename extension is missing or misleading.

The “89a” portion identifies the later major GIF specification released by CompuServe. The earlier GIF87a version begins with `GIF87a` instead. GIF89a added features including graphic-control extensions, transparency, animation timing, and application-specific metadata, although looping conventions such as the Netscape extension were developed separately.

A common mix-up is to treat GIF89a as a filename extension or as the name of an animation format. It is actually the header identifying the GIF version; both still images and animated files can use it.