By using the keyword signature (not to mistake with a similar keyword, freesign), you can apply the signature of the connected user automatically in a field.
When this kind of field is empty, you will need to sign in order to save a signature to the user's profile. Once the signature is saved, it will automatically be applied to all signature fields.
Once the signature is saved, you need to follow those steps in order to reset it:
Enter a form in production where there is a signature field.
This procedure cannot be completed from the Editor mode;
Enter the signature field.
If a signature appears automatically, you are indeed in a signature field.
If not, you are in a freesign field, which does not apply to this procedure;
In the signature window, tap on the lock in the top right corner;
If you haven't left the form since you signed first, you will just need to enter your password to unlock the signature;
If you have left the form after signing in the field, you will need to enter a username and password to unlock the signature.
An administrator or the person who signed can enter their credentials to unlock the signature;
After unlocking the signature, tap on the hyphen icon ("-");
Your signature will be removed.
Tap on Sign here in the middle to create your new signature;
After signing, tap on OK to confirm;
Your new signature is now saved in your profile and will be the one used in the future, or until you repeat this procedure!