In general, citrus fruits symbolize cleansing and purification.
Oranges and lemons, in particular, represent joy, happiness, and the abundance energy of the sun (think summer light and warmth!)
Orange: Joy, happiness, purification, money, luck.
Lemon: Longevity, happiness, refreshment/rejuvenation, purification, money, physical energy.
Lime: Protection, purification.
Grapefruit: Purification.
Tangerine: Purification, magickal energy.