What do the words mean?
Aranach Ba-it Esetatvani
Becoming invisible to hostile intent
Narechpa Usavi Klivaset
It's a command: return whence you came
The Sigil to Become Invisible to Hostile Intent has these words that bounce energy back. The invisibility is there because you become a mirror and all they see is themselves — as type of stealth technology. Makes sense? Sign the sigil and say those words and intend invisibility.
How to Dispose of Black Magical Objects
How would one dispose of black magical objects? Can you just bury them in the earth? Perhaps with the sigils against ill intent?
Your suggestion is absolutely correct.
✶Note: the Sigil to Become Invisible to Hostile Intent was recently corrected (see the 3 vertical dots), while the Sigil Against Ill Intent was updated in the download to include its three-word incantation.