Not your, you're, it's a contraction, knowing the distinction shows you're skills are awesome.
It's what I want to see when I look at your job application materials. If you don't have any, or can't show it, I can't appreciate that you are awesome and therefore won't follow up to talk with you.
If you don't have a github (or whatever online presence is being sought after), you'll lean more heavily on places that use a CV, or through your network. Getting in through a network probably means you don't need the github.
Conversely, if you have an awesome github and an awesome network, then the fact you have a github is moot (unless people only know you because of it). You'll get hired anyway.
So the github only really matters for the portion of people who don't have a network, and are applying for companies who care about code they can review before you even talk to them, which is mostly the HN bubble, and not any megacorps.
Github demonstrates knowledge of (1) current trends in open source, (2) using source control, and (3) a project that can be looked over.
(Substitute github with bitbucket or whatever, I don't care that much).
With respect to engineers who are under restrictive IP contracts, all I can say is I'm sorry. You are likely to be shown up by others who demonstrate skills in ways you are unable (by contract) to. Do your best to leave and find a place where you can demonstrate your awesome.