For me, it's having a successful blog that is on topic to the position. When I started my current job 7 years ago, I started a blog then which was simply a repository of lessons learned, scripts I can reuse in the future, cheat sheets, and videos. I still use it today to look up how I did something years ago, but apparently a lot of other people use the site too. The blog demonstrates the following to any potential people willing to hire me:
* A sample of my writing skills * A sample of my design skills * A sample of my engineering skills (shown in scripts and codes) * A sample of my documentation skills * Additional proof that I am passionate/skilled/interested about this type of work.