It is time to fight back in a big way. Several years ago, I sent my assistant out to purchase Christmas cards for my business. She came back with several samples, none of which mentioned the word Christmas. It was all "Happy Holidays" or "Season's Greetings". I told her I wanted cards with Christmas specifically mentioned as the focus. She said "oh no, you can't do that. It might offend someone." I told her "if it offends someone I'm Happy! Now go get some Christmas cards."
If someone tells you they don't believe we should celebrate Christ at Christmas, tell them to just skip the holiday because that's what its all about!
I intend to sign with a note saying that I am celebrating Christ's birth and wish everyone the happiness that I am experiencing.