A good martial artist always hides themselves. All warfare is based upon strategies of deception, misdirection and the element of surprise. Our opponents can only defeat us if they are more prepared than us or are somehow aware of our intentions or tactics.
In the old days there was a lot of fighting going on. Simultaneously, there was competition for students and people came to schools in order to defeat them to make a name for themselves. When someone went to the school in either of these contexts, it was called dojo yaburi or to "break" the dojo. If they defeated the teacher then they could take over the school or use that win to find a job. The modern definition of the word yaburi means to escape, but in an older context it was defined as yaburitoru or "to break or rip in half." A common occurrence after one won was to break the former teacher's kaban or sign in half.
Because someone might want to attack, a good warrior smartly never demonstrated their techniques in public and never drew attention to themselves. A good rival studies their opponent's every move in order to gain an understanding of how to defeat them. A good martial artist, therefore, always keeps themselves hidden.
Yesterday I posted a video of 27 different people being robbed on a street corner in Rio de Janeiro. Most were minding their own business when they were robbed by these hoodlums who were just hanging out waiting for unsuspecting and distracted people to walk by. When an easy mark walked by, they would snatch something like a necklace or a phone and run away. The people who were are aware almost never got bothered.
Today, nobody comes to a dojo to "break" it, but this doesn't mean we can let our guard down. No matter where we are, we can be attacked. A good martial artist knows this and hides themselves because they never know who might be watching or who wants to attack them. When we practice we are supposed to be aware of our surroundings so that we don't fall or hurt someone. Likewise we are supposed to exercise this awareness as we go about our normal day. A good martial artist is never surprised because they are always aware and thus always one step ahead.