Some forum owners might not mind having "special characters" at the beginning of their thread titles but some do. Users use them so that their thread stands out from the crowd.
It would be great to have something in settings so that the admin can choose
allow special characters in thread titles
allow special characters but not at title start
never allow special characters.
This can always be coded as a plugin but it seems like a really easy thing to put in the standard code that will help a large number of forum admins.
BTW: I put them in this thread title as an example