Add Notification to Magento 2.3 Customer Registration About Shipping Restriction to California

I want to add a notification that appears on the registration page – only when California is selected as a state. Otherwise it will not display. I am unsure of the parameters. I am using Magento 2.3

The current code on the registration.phtml is the following:

                < ?= /* @noEscape */ $block->getAttributeData()->getFrontendLabel('region') ?>

                    
                        < ?= $block->escapeHtml(__('Please select a region, state or province.')) ?>
                    
                    

                

and my PHP is this, which isn’t working:

< ?php if ($region_id == '12') {echo '
Please note: We do not ship to California.