How do I configure RT to not accept signature (vcard) attachments

To list,

I’ve finally determined where this VCard attachment is coming from.
Apparently, our Gmail offers the user the ability to attach a signature
verification attachment to the email. I guess this is so people will know it
is not spam or something.
Anyway, I don’t want RT tickets cluttered up with these Vcard attachments.
How do I get RT to drop them. We don’t need them.