Yom Kippur is a solemn and reflective holiday, so it is not customary to greet those observing with "Happy Yom Kippur". Instead, appropriate greetings should focus on meaningfulness and reflection. Here are some common greetings to wish someone observing Yom Kippur:

• "Have an easy fast" or "Tzom kal"
• "Good Yuntif" or "Yom Tov" (Yiddish and Hebrew, respectively, for "Have a good holy day")
• "Gmar hatimah tovah" or "Gmar tov" (which roughly translates to "a good seal")
• "Ketiva vchatima tova" (which means "have a good writing and sealing")
• "May you be sealed in the Book of Life"

It is also appropriate to wish someone a meaningful Yom Kippur.