Ave!
IHS or visa versa, is a
Christogram - a combination of letters that represent the holy name "Jesus." Early scribes would abbreviate the sacred names of Jesus by using the first two letters of the name, or the first and last letters. For example, the Greek letters
Chi-Rho (which looks like our English X and P) was an abbreviation for the name "
Christ." Likewise, I (iota) and H (eta) are the first two Greek letters for "Jesus." Sometime in the second century, the third letter, S (sigma), was added, thereby rendering IHS or SHI.