Based on the act of writing:
* Erasure: This is the direct opposite of inscription, as it involves removing writing.
* Deletion: Similar to erasure, but can be used for digital or abstract concepts.
* Blankness: A state of being without writing or markings.
Based on the content:
* Anonymity: The absence of a name or identifier, the opposite of a signed inscription.
* Secrecy: Keeping something hidden or unknown, the opposite of an inscription that makes something public.
* Silence: The absence of words or communication, the opposite of an inscription which conveys a message.
Other possibilities:
* Removal: A general term for taking something away, including an inscription.
* Destruction: Destroying or obliterating something, including an inscription.
The best antonym will depend on the specific meaning you want to convey.