Country
Since the Xbox Live network connects players from more than 100 countries, you can count on playing against people who aren't from the same country as you. Express your inner patriot with a modded gamer tag that features your country's flag or other national symbols. If you are playing in Russia, for instance, you could use a bear. If you are a British gamer, you could feature the George cross, a symbol of British nationalism, or John Bull, a man who serves as a personification of England.
Job
Another identity-related gamer tag idea is to create a tag related to your job. If you work in construction, use a hard hat or a bulldozer in your modded gamer tag. If you are a teacher, put an image of an apple and an A+, a chalkboard or a stack of books on your tag.
Music and Movies
Even if you are too busy sniping your opponents to chat about entertainment with them, you can still show them that you are a diehard Metallica fan or a true-blue Deadhead with a modded gamer tag. You can also show your love of "Star Wars," "Harry Potter" and other popular film series with movie-themed gamer tags.
Eclectic Options
Sometimes the best option is to just let your creative instincts take over. Anything from a silly image of a man wearing a tacky mustache to a Teletubby or other children's character can surprise your fellow players and engender a few laughs. Other amusing options for you to consider include off-kilter political messages ("Chuck Norris for president") and quotes ("I think, therefore I am depressed"). A really strange modded gamer tag may even distract your opponents during a heated battle and earn you extra kill points.