Run the ecconv command with the wanted stamp text and color:

ecconv -export tif -compression lzw -stamptext “Do Not Use” -stampcolor inverse INFILE OUTFILE

For further information on stamp options, run:

ecconv -help

To put the stamp at a slightly different angle (following image diagonal) you can set an environment variable before running  the command.

Linux:

export ECSIMPLESTAMPANGLE=1

Windows:

set ECSIMPLESTAMPANGLE=1