Wiktionary
unsign
vb. 1 (context transitive intransitive English) To remove one's signature from (something one has signed). 2 (context of a state, or those acting on behalf of a state English) To declare void one's signing of (a treaty).
Usage examples of "unsign".
Hughes-Beckett, if it was indeed he who had sent the telex, which was unsigned and had no indication of origin, was up to his old tricks of seeming to help while encouraging failure.
The note was unsigned, but despite the bold, dashing handwriting, more suited to a man than a dainty little lady, she knew who had written it.
Is it fair to attribute responsibility to an unsigned journalist--for what he has to say?