I have seen this before on online rpgs/forums 1337>LEET means "Chat room language" or "Elite" its like 666 is known as devils number although we cannot read it as a word lol.
The 'language' itself (if you want to call it that) is essentially based on typing using only non-alphabet characters. Example: if one was to say, "hello, my name is" in order to place it in these such characters it would look more like "#3||0, /\/\'/ /\/@/\/\3 15".
Usually, it isn't used in such a grotesque way because 1337 would refer to the nature of internet typography where some internet users would intentionally spell words using numbers inside (and also creating intentional typos).
Most people above 12 seldom use this apart from tiny gags.
