NeoDesk icon is an icon format associated with the NeoDesk graphical environment for the Atari ST family of computers, developed by Gribnif Software.
As far as we know, the format has not been decoded. It is reported to be compressed, and "complicated". That said, some .NIC files are clearly uncompressed, so evidently there are multiple .NIC formats.
Compressed .NIC files apparently begin with the ASCII signature "
Uncompressed .NIC files either have no signature, or possibly always begin with bytes
00 00 00 00.