Your Invitation

I cannot keep quiet about this. I saw a sign today that said:

Your invited!

This abuse of grammar must stop! This sign was probably written by a student in high school, but I saw the same thing on a flyer which my son brought home from school, which I assume was typed by his teacher. She should know better. How can she teach grammar to my son if she doesn't know this should say,
You're invited,
which means you are invited. "Your" is a possessive pronoun. I don't own an "invited." I actually couldn't, as it is a verb, not a noun!!!!!

So please use the correct grammar on your invitations.

Thank you!