I've been a big fan of Mike Aquilina. His book The Mass of the Early Christians is becoming a classic, and it's one of those titles that you should have on hand for apologetics.
Last year he came out with a great book entitled: Signs and Mysteries: Revealing Ancient Christian Symbol. It is beautifully illustrated by Lea Marie Ravotti. Aquilina examines ancient Christian signs - things that you've seen in one hundred different churches, on vestments, and emblazoned on altars, but never understood. The style is engaging and the artwork is very well done.
During the Advent and Christmas seasons, many Christian signs are employed and this would be a great guidebook in helping you and others understand their meanings. Please visit the amazon page and grab a copy or two. You won't be disappointed.
While you're at it, check out Mike's blog: Way of the Fathers.