Billboards are a great tool for companies that want to expose their job openings to a broad array of people and get a lot of exposure quickly.
They can be especially effective if there is a billboard in a geographically significant region to your business.
Ultimately, you will have to have a conversation with your team about your goals to determine if a billboard is the right move. If your open job position and company message can be simply expressed and understood within a few seconds, then a billboard can be a great tool.