That’s what HelloBar is designed to do.
It is a free tool that places a frame at the bottom of your site and can either promote a page, your phone number, social media account or collect email signups. It works with providers like Mailchimp so you can sync your lists.
I use the free version on RecruitingHeadlines to call attention to upcoming webinars. But if you want all features you’ll have to pay for the premium version. Either way its a great tool that is fairly non-intrusive to your user experience.
For job boards it could be a great way to funnel your visitors into signing up or collecting an email.