As with Hidden in Plain Sight, I found the flag within the provided file’s metadata, under the “Encoded By” field:
exiftool message.mp3
ExifTool Version Number : 13.25
File Name : message.mp3
Directory : .
File Size : 241 kB
File Modification Date/Time : 2025:06:14 09:06:48-07:00
File Access Date/Time : 2025:06:14 09:07:14-07:00
File Inode Change Date/Time : 2025:06:14 09:07:13-07:00
File Permissions : -rw-rw-r--
File Type : MP3
File Type Extension : mp3
MIME Type : audio/mpeg
MPEG Audio Version : 1
Audio Layer : 3
Audio Bitrate : 64 kbps
Sample Rate : 44100
Channel Mode : Single Channel
MS Stereo : Off
Intensity Stereo : Off
Copyright Flag : False
Original Media : False
Emphasis : None
ID3 Size : 79
Encoded By : C1{metadata_tells_more}
Encoder Settings : Lavf61.7.100
Duration : 0:00:30 (approx)
C1{metadata_tells_more}