How can I restrict special symbols (@,#,$,%, etc.) for a custom field in Jira SM? (ScriptRunner)

[Nick]

I create a custom field "Job title" and make it visible in the customer portal (Jira SM). How can I use ScriptRunner to restrict special symbols (@,#,$,%, etc.), and is this even possible?

I know I can use regular expression ^[A-Za-z0-9 ]+$ as a validator, but that's in the workflow settings. I need to put a restriction on the custom field that should be displayed in the customer portal.