LATACINT
ersatz
anonymous
There are total of 9 letters in this word.
Call Letters
Not sure if this is the word you seek, but another word for "last name" is surname.
In the context of diamonds, the letters CT are used as a substitute for the word carat. Diamonds are weighed in carats.
an anagram
Letters that stand for parts of a name are called initials.
An anagram is a word puzzle. You rearranging letters to create a word, phrase, or name. For example, the anagram of the letters nrdife spell the word friend.
Read the context to find possible words; use the word length and shape to find possible letters. If that fails, wing it and substitute a new word.
typewriter
A bird