I just made an entry for this in the "user submitted names" section but thought I'd post it here too:
This very rare name is an exception to the rule that numerals are normally not allowed as part of the spelling of names in the United States. It's a creative rebus-like spelling of a slang intensive term for "tiny" found in the Southwestern United States. Most Americans would be familiar with terms like "teeny-tiny", "teensy-weensy", etc. "Teeninecy" is a rare variation of these that's found in the Deep South, and as a rare slang term it doesn't have a set spelling, with teeninesy, teeninetsy, teaninesea, and many others being found. Though a couple of other spellings have been used as names, T9C seems to be the most common in that role. It probably began in Texas in the 19th century as the earliest examples found so far are from that state.
Here is an example of a woman named T9C, T9C Phillips Dinterman, who recently died in Maryland. As you can see from the obituary article, her name was supposedly suggested by a
Baptist preacher from Texas, which fits the part of the USA (Texas and Oklahoma) where most other examples of T9C have been found:
http://www.heraldmailmedia.com/obituaries/a_life_remembered/t-c-p-dinterman/article_18edafe4-cd7b-11e3-8d6c-001a4bcf6878.html
As I said in the notes to the submission, one reason I wanted to post about this name on "Behind the Name" is to counter some of the false urban legends that are already in circulation about it. It's not something taken off a can of fertilizer, it's not from a math formula, and it's certainly not the serial number of a World War II bomber because many examples are older than World War II.
I think this is a fascinating name myself as an example of something which seems to break the rules of normal spelling and yet has been accepted as an official name on more than one occasion.