Here's how you would sign the concept of Christmas in ASL:
1. "Xmas" sign: This is a common sign for Christmas. It's made by forming the letter "X" with your index fingers and thumbs, then touching your chest.
2. "Holiday" sign: You can also use the sign for "holiday" which is made by signing the letter "H" with your dominant hand and moving it forward.
3. "December" sign: You can sign "December" and then the number "25" to convey the date.
4. "Santa Claus" sign: If you're specifically referring to Santa Claus, you can sign the name.
5. "Christmas tree" sign: You can sign "Christmas tree" which involves signing "tree" and then a gesture of a tree with your hand.
The specific sign you choose will depend on the context of your conversation.
Remember, ASL is a visual language and signing involves both handshapes and facial expressions.