Could it be an acronym for the church he once attended, not the one where he is buried? ie: Zion Valley Baptist Church or something similar? Maybe he was buried in a cemetery different from that of where he once worshipped. Or he's actually buried elsewhere and the stone you see is a memorial marker only. The numbers indicate where he is buried in the other cemetery?
Could it be a military designation or number from the civil war, like a Zouaves Regiment or something similar?
or something similar to this inscription from the US genweb WVa Tombstone site, where zbrc means Zella Bly Ross Crews?
Crews Henry Edward Zella Bly Ross 1886 – 1960 1888 – 1985 H. E. C.Footstones: Z. B. R. C.