Gender-neutral "Jane Doe" / "John Doe"

Is there a gender-neutral alternative to "Jane Doe" / "John Doe"?

I would like to provide an example of signed form, but how to avoid using gender when it comes to names? Is there some widely-used idiom for this?

Solution 1:

A. N. Other

Proper noun
(British) A formulaic name that is substituted for that of a person whose name or identity is not known, or not relevant; typically used when exhibiting an example.
— wiktionary.org

Here is an example copied from freshdesk.com :

And a similar definition from macmillan :

a member of a sports team who has not been chosen yet, so that you cannot give their real name in a list of players

Solution 2:

The most fitting name to me for non-binary is "Jay Doe." It is important not just to use the letter. The problem is that the letter J is used genericly for a person of unknown sex or gender and could become confusing when heard (J and Jay sound the same).