I am sorry but the PC police are rediculious. I wasn't able to say happy easter on my door while I worked in a preschool. I actually had a few parents ask why I took the art work off the door and changed it for happy spring. I told them that I got in trouble for putting Happy Easter up on the door.
I say go with merry christmas or ask if there are any residents that celebrate a different holiday and you can make one special for them that says happy your holiday and if you can put their name on it all the better. You have to label label label with residents name on everything. My granny is in one and everything including her socks have her name on them.