The Number and the Badge
In most sports a number is an accident of what was left in the kit bag. In soccer it is closer to an inheritance. A club's number 10 carries an argument about who the team is; the 9 is a job description; the 1 belongs to whoever is willing to stand alone. Players know exactly which number they are, and they usually know exactly why.
That is the reason so many engravings on the back of a soccer pendant are two characters long.
Three things people engrave
The number. One or two characters, cut into the back plate. It reads as nothing to a stranger and as everything to the person wearing it. If you are buying for someone else and you are not certain of the number, this is the one detail worth asking about — the wrong number is worse than no engraving.
Initials. Also short, also private. Common for a player who has changed clubs enough that no single number has stuck, or for someone buying for a partner rather than a teammate.
The badge. A club crest is the longest-running version of the same idea — a mark that says which side of a city you are from. Crests are engraved from artwork you send, and you see a proof before anything is cut.
The practical part
Engraving sits on the back of the piece, so the front stays the clean field design. There are three tiers: one to three characters, four to ten, or a crest. One to three is right for a number or initials; four to ten covers a name, a date or a short phrase.
Five fonts are available — Arial, Palatino, Monotype Corsiva, College Block and Times New Roman. Block styles hold up better at one or two characters; the script faces read better across a full name.
Chains come at 18 and 20 inches. Twenty sits lower and is the more common choice for everyday wear over a shirt; eighteen sits closer to the collarbone.
What it has to survive
A soccer pendant that only works off the pitch is a piece of jewellery, not a piece of kit. These are 316L stainless steel — waterproof, sweat resistant and tarnish resistant, in a polished steel or 18K gold PVD finish. Training, rain, a season of it.
The point is not that the engraving is visible. It is that the person wearing it knows it is there.