I think this is a bit exaggerated statement, but it cost you nothing if you think for your own safety then I guess keeping it secret is perfectly fine.
What I was thinking is that, wearing expensive jewelries is far more susceptible to street criminals than simply wearing a bitcoin tees. I personally saw several people wearing bitcoin logo from tees, pants, car stickers, and even tattoos and I don't think they are having problem with it. Fortunately, I live in a small city where crime rates were not to high compared to the big cities in my country, but honestly I have not heard of a crime regarding someone was killed as stealing bitcoin being the primary motive.
I wore a bitcoin logo several times already when I visited big cities here and in some tourist destinations where there are a lot of foreigners, but none even once was I asked about it.