A brand could be a personal portfolio that can be used outside the company for entrepreneurial endeavors.
So there might be issues with this. For your portfolio to be effective, you probably need some screen shots. This is "eye candy," that gets people interested if and when they give it a 5 second glance. Most companies don't care, but if it's an internal application, they might.
Having said that, you are always promoting (or demoting) your brand. People you work with notice your ability and work ethic always. When those people go to other companies and their new boss asks, "Do you know anyone who is good and will fit this role?" You want them to mention your name. You do this by always giving good effort. People definitely notice. I've gotten tons of jobs that way.
All of this requires time.
Maybe there are some limitations due to a nature of your contract? In one of my contract it explicitly said that I have a right to showcase the work that I've done as a contractor in my portfolio. I guess that this means that maybe in some contracts people get the opposite thing.
I've never tired to build my personal brand beyond basic presence on web. The main reason is lack of time. I wish that I've been smarter and build it along the way, if nothing else for myself. I've started forgetting all of the wonderful things that I've worked in past decades.