Alpha (A) and Omega (Ω) are the first and last letters of the Greek alphabet. These letters are often reproduced on gravestones, and when displayed separately Alpha is depicted on the left and Omega on the right.
Frequently the letters are combined to create a recognized Christian symbol derived from the book of Revelation in which they are mentioned in separate verses.
1:8: “I am the Alpha and the Omega,” says the Lord God, “who is, and who was, and who is to come, the Almighty.”
22:13: “I am the Alpha and the Omega, the First and the Last, the Beginning and the End.”
They are commonly used in conjunction with a cross, a crown or the Chi-Rho (a monogram of chi (Χ) and rho (Ρ) which are the first two letters of the Greek word Khristos.
On a side note, there is a cemetery in Henderson, Vance County, North Carolina, USA which bears the name Alpha Omega Cemetery.