That’s what you hear from some people how many, no-one can be certain. It is not that Jews are generally ashamed of their Jewishness, but simply that sometimes it is easier not to have to explain everything about yourself.
There may be long periods of years when you can manage not to reveal your Jewish identity, but in most cases it becomes known sooner or later.
A different philosophy motivates some Jews, especially men, who may well wear a kippah all day, however inconspicuous, and even let their tzitzit be visible.
If this is what a person wants and can cope with, fine. But as the sidra reminds us, tzitzit and other outward signs of Judaism are chiefly reminders to ourselves, not necessarily announcements to the world.
That does not mean that a person is exempt from tzitzit or kashrut or anything else, but the words of the Torah make it clear that, in relation to tzitzit, their purpose is “that you may look upon it and remember all the commandments of the Lord and do them” (Num. 15:37-41).
The outward reminder is to ensure that I myself am well aware of my Jewish identity and what it requires of me, namely “to do justly and love mercy and walk humbly with God” (Micah 6:8).
Whether people see my tzitzit or not, they should see that I am a person who is honest, fair-minded, truthful, decent and reliable. That goes a long way towards being a Jew wherever I go, whether I advertise my Judaism or not.