If you refrain from a permitted action because Jews
might see you and think you're really doing some other (forbidden) action,
'Ayin. You should refrain from these actions because your fellow Jew might think the action they think you're doing is OK. This is like the
case of driving to the hospital on Shabbat.
On the other hand, if you refrain from an action because non-Jews would see you and criticize the Jewish people, thinking you're violating
halachah (such as going into the McDonalds restroom), that's a case of avoiding Chillul Hashem.