Special Values - widberg/fmtk GitHub Wiki
UNDEFINED_FVALUE
The Zouna engine has defined a constant UNDEFINED_FVALUE to represent an undefined float with a value of -1612.0 or 0xC4C98000. I do not know why they chose to define their own value for this instead of using one of the IEEE 754 NaN representations.
Data Type Limits
Wikipedia has a handy list of data type limits.
Often values of 0x00 and 0xFF, the minimum and maximum values for an unsigned 8-bit integer, are found in padding in files.
Debug Values
Wikipedia has a handy list of debug values.
Notably, 0xCCCCCCCC, 0xCDCDCDCD, 0xFDFDFDFD, and 0xFEEEFEEE are used by MSVC to mark uninitialized/free'd memory. These sequences are often found in blocks of padding in files.