code: public UserSignature updateSignature(String accountId, String userId, String signatureId, UserSignatureDefinition userSignatureDefinition) throws ApiException {
      return updateSignature(accountId, userId, signatureId, userSignatureDefinition, null);
    }
docs: Updates the user signature for a specified user.
  Creates, or updates, the signature font and initials for the specified user. When creating a signature, you use this resource to create the signature name and then add the signature and initials images into the signature.  ###### Note: This will also create a default signature for the user when one does not exist.  The userId property specified in the endpoint must match the authenticated user&#39;s user ID and the user must be a member of the account.  The &#x60;signatureId&#x60; parameter accepts a signature ID or a signature name. DocuSign recommends you use signature ID (&#x60;signatureId&#x60;), since some names contain characters that do not properly encode into a URL. If you use the user name, it is likely that the name includes spaces. In that case, URL encode the name before using it in the endpoint.   For example encode \&quot;Bob Smith\&quot; as \&quot;Bob%20Smith\&quot;.
  @param accountId The external account number (int) or account ID Guid. (required)
  @param userId The user ID of the user being accessed. Generally this is the user ID of the authenticated user, but if the authenticated user is an Admin on the account, this may be another user the Admin user is accessing. (required)
  @param signatureId The ID of the signature being accessed. (required)
  @param userSignatureDefinition  (optional)
  @return UserSignature