HS students are the same way. Remember that these are the
symbols that are meaningful to their culture (that culture being
American Teenager). It sounds like you're doing a good job of
presenting the history and use of symbols in different cultures
(and Sandra suggested some more). Those symbols, while exotic to
us, really meant something to the cultures that produced them.
With that in mind, when you see the ying-yang or smiley face,
approach it by asking what it means to the student. If they say,
"I don't know" or "I just like it," then suggest they rethink why
they want to use it. If they can come up with a reason for using
it, I just go ahead and let them (and grind my teeth a little).
A whole field of that stuff can actually look pretty interesting
if they put a little thought into it (reversals, tesselations,
With those sports symbols, I tell my students that the team logos
are someone else's artwork and are copyrighted, therefore, they
can incorporate the idea of a bull or cardinal, but they must
change it so it's their own artwork. It's easy enough to
incorporate the team colors (I see a lot of purple and orange :P
because of the Phoenix Suns). If it's the sport, rather than a
particular team, I have no problem with blazing basketballs or
crossed baseball bats--it's what's important to them.
After I finish grinding my teeth, I remind myself that personal
expression in art is what we're after, and these symbols are, for
better or worse, a part of that. They outgrow it eventually.