People back in Biblical times didn’t have their clothes monogrammed (so far as we know) but if Jesus had been so inclined, He could have had several designs to choose from! All kidding aside, the early Christians did develop a number of specialized monograms/logos to represent the person of Jesus.
Probably the most familiar is the ‘fish’ logo that you see displayed on car bumpers and many other places (as in the Fish Hooks logo above). Though most people recognize that this is a Christian symbol, a lot fewer have a clue as to why. Of course, any reader of the Bible is well aware that many of the Gospel stories involve fishing. We also remember that Jesus invited His disciples to be “fishers of men” and performed one of His greatest miracles when two small fish helped feed a crowd of over 5000 (Matthew 14:17). Potent though those associations are, they’re not the reason for the symbol: rather it comes from the fact that when you take the first letters of the Greek phrase: “Ἰησοῦς Χριστός, Θεοῦ Υἱός, Σωτήρ” (meaning “Jesus Christ, Son of God, Savior”) you get ΙΧΘΥΣ (ichthys) which is the Greek word for “fish.” Thus, this crude symbol became a compact identification code in a time when it was dangerous to acknowledge being a Christian. It is said that a believer meeting a stranger on the road might casually scrape an arc in the dust. If the other then completed the fish by drawing the complementary arc, both knew that they were speaking to a brother in Christ.
The “Chi-Rho” is one of the oldest and most universal monograms used for Jesus: it is simply the Greek letter “chi” superimposed on the Greek letter “rho.” These are the first two letters of the Greek word ΧΡΙΣΤΟΣ (Christos) which we say as “Christ” in English. Even prior to Christianity, the chi-rho symbol was an abbreviation for “very good” that was sometimes written in the margins of documents to call attention to particularly important passages. Perhaps it was this usage that encouraged the early Christians to adopt it as their own symbol for Christ. When the emperor Constantine adopted Christianity in 313 AD, the Chi-Rho (also called the Chrismon or Laberum) was employed as a symbol on the shields and banners of his army as well as the coins of his realm. Unlike the fish symbol, which largely dropped out of sight after the early Christian era and reemerged as a popular symbol in the 1970s, the Chi-Rho has enjoyed a long and continuous career as a liturgical symbol.
This representation (often called the “divine monogram”) is used extensively in both Roman Catholic and Protestant churches, where it appears on altar cloths, stained glass windows, and liturgical vestments. However, despite its popularity, it is perhaps the hardest to explain. To begin with, the two versions shown are but a sample of the many that one might encounter. It is supposed to represent the first three letters (iota-eta-sigma) of the name of Jesus in Greek: ΙΗΣΟΥΣ, but it is almost always expressed in Latin letters where, because of ambiguities in conversion from the Greek alphabet, the first letter is rendered as either I or J and the last as S or C, so you may see IHS, IHC, JHS, or JHC. These letters have then been commonly reinterpreted as representing a variety of Latin phrases such as “Jesus Hominum Salvator” (“Jesus, man’s savior”) or “In Hoc Signo vinces’ (“in this sign you will conquer”). When the monogram was used in English-speaking churches, it acquired yet further interpretations such as “Jesus Holy Savior” and “In His Service”. (Unfortunately, the JHC form is also thought to be the basis for the expression “Jesus H. Christ” sometimes heard as an expletive.)
Alpha and omega are the first and last letters in the Greek alphabet. When God describes Himself this way in the opening verses of St. John’s Revelation: “I am the Alpha and the Omega … who is and who was and who is to come, the Almighty.” (Revelation 1:8) He is echoing His even more ancient pronouncement to the prophet Isaiah: “I am the first and I am the last, besides me there is no god.” (Isaiah 44:6). So when Jesus makes the same statement at the end of John’s vision (Revelation 22:13) He is confirming that He is eternal God with the Father. Thus, this pair of letters powerfully expresses the eternal divinity of Christ.