add_custom_validations.js

// Replace the values in `fieldLabel` and `field` with the field you want to add validations too.
// This example shows how you would require Organization.

$(document).ready(function() {
  var fieldLabel = $('label[for="subscription_customer_attributes_organization"]');
  fieldLabel.text(fieldLabel.text() + " *");
});

var field = $("#subscription_customer_attributes_organization");
var form = $("#signup-form");
var submitBtn = $("#subscription_submit")

submitBtn.click(function() {
  if (field.val() === "") {
    field.parent().addClass("has-error");
    field.parent().append('<span class="error-message">cannot be blank</span>')
    return false;
  }
});

form.change(function(){
  if (field.val() != "") {
    submitBtn.click(function() {
      return true;
    });
  }
});

field.blur(function() {
  if ($(this).val() !== "") {
    $(this).parent().removeClass("has-error");
  } else {
    $(this).parent().addClass("has-error");
  }
});