The only way you'll know with certainty is to use a acid test kit.
A hallmark does not guarantee karat gold, I've seen fake hallmarks.
This is how I usually test karat jewelry.
Test it with a magnet, if passed I will look at it with a loupe for hallmarks and give a careful look at the corners of the article to see if the plating has worn and base metals are showing through.
If all is ok with the first two tests, I use a touch stone and acid test kit.
Very little fake jewelry can get past a acid test.
I was thinking the same thing, but it really looks like a J. That's not a serif of any kind on the bottom of the "T".
If it is a J, it's not any kind of standard marking that I've ever seen. I could come up with some theories (non-European/US attempt at "14KT", ring is 14K and "J" is the maker's mark, they made a boo-boo and stamped over it, etc.), but the best thing you can do is test the metal.
The best I could find for the 14KJ was that "apparently" it's solid 14k (yellow gold), according to a few auction sites with the same 14KJ marked items on it.
Answers.com says that it just means that it's 14k gold.
I'd get it tested to be sure. If you take it somewhere, make sure they test the clasp AND chain itself, because there's always the small chance, that someone switched it.
Edit - If it actually is 14k Yellow gold, it'll be something like this.
Some web searching will take you to listings of common gold alloys and their typical components. Keep in mind these are ballpark--you can vary the other additives to change the color, and the only thing that matters in the end is the gold proportion.
There can be only one! @xxxx[::::::::::::::> :twisted: :mrgreen: "Highlander movie reference"
At least you didn't ask him about switching his car insurance :lol:
Just like upcyclist said, it can vary, but if alloy percents are switched too much, it wouldn't be considered "yellow gold" anymore. There's alot of websites that have information about the types of alloys.