Yes - it turns out the signature looks familiar if you decode it:

```
In [1]: FITS_SIGNATURE = (b"\x53\x49\x4d\x50\x4c\x45\x20\x20\x3d\x20\x20\x20\x20\x20"
   ...:                   b"\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20"
   ...:                   b"\x20\x54")

In [2]: FITS_SIGNATURE
Out[2]: b'SIMPLE  =                    T'
```

This is the same approach taken in Astropy. The signature isn't *required*, it just means that if a file starts with this, then it positively identifies it as a FITS file. I think the FITS standard requires FITS files to start with this.