It exists as a concept or you wouldn't be able to ask this question.
I'd say that for relativists/post modernists all logic would be considered subjective.
If you're asking if Ti as a concept exists in the canon of philosophy the answer would be "don't think so, its a socionics construct and socionics leans more towards psychology than philosophy" Also "socionics is an obscure topic and even philosophers wouldn't try to define terms from it"
That being said: "cogito ergo sum" is the quintessential example of subjective logic. It's truth is proven by it's self-reference. Even though it's supposed to be something that is universal, Descartes' main point was that HE couldn doubt so there was something (he) that was able to doubt (read the book if you think I mistranslate "cogito").
Idealists in general use "subjective logic" to prove all kind of stuff. Berkely has an interesting maxim about the existance of god (everything exists only if it is observed, since not everything is observed by something all the time that would mean that stuff stops existing if you don't look at it. That's absurd...so....god exists, he's the thing that observes everything all the time).
oh well.. enjoy