What are you guys talking about? The Cleric of Shar isn't wearing symbols of Shar, they're just black circles that happen to look exactly like a symbol of Shar. Why would you think they're symbols of Shar?
Which oddly enough aren't bordered in purple. But details, whatever.
Regardless, the argument isn't that they don't symbolize Shar to Shadowheart.
The argument is that people are more clever in hindsight than they are before.
The argument is that, if you don't know she's a cleric of Shar, then they look decorative, not suspect.
The argument is that people wear onyx jewelry, and that no one would accuse anyone of being devoted to Shar simply because they're wearing onyx.