Ok, I think I get it now. Badges are not all that formal, just a sign of "I'm a (insert family name here)". I really am not sure how coat of arms got brought up with this but I don't really have any interest in a coat of arms, just knowing what badge would be the most appropriate.
In order to understand the symbolism behind a clansman's badge in Scottish heraldy, it is necessary to discuss coats-of-arms and the peculiars of Scottish heraldry.

St Andrew's cross would not be my first choice but getting into religion vs catholicism vs christianity. I would much rather have a simple "I'm a christian".
The St. Andrew's Cross is the national symbol of Scotland, and a "non-denominational" one as well -- as I said in my earlier post, it is found on the national flag, and is worn by many as a sign of their Scottish heritage, regardless of denomination.

Apologies for the confusion. It was not my intention to offend.

T.