You do not need to sign up for Community Gifts! You just need to either leave a prompt at the link, or, when the prompt list is posted, create your fill and have it posted in the collection by the end of December 26th. (You don't need to both prompt and fill if you don't want to; whatever combo of prompts/fills suits your fancy is fine.)

A more complete guide to Community Gifts is available here (http://cap-ironman.livejournal.com/1619340.html). Thank you for reminding me to go link it in the relevant points in this post :D

Edit for clarity