BTT is weird and inaccurate to use because it does not match with the full name of forum, Bitcointalk that I even more prefer to use than BCT or BT. I have no issue to write a full name of forum, Bitcointalk and see no reason to use its abbreviation like BCT or BT.
While your reason is clear for using the BCT abbreviation instead of BTT, I am use to seeing BTT than BCT in the forum. I am more conversant with BTT or BT than BCT. When I was reading the OP’s post, for a while I thought he wanted to say BTC and mistakenly wrote BCT. BCT will be confusing to use in the forum since its abbreviation is almost the same as BTC. BTT or BT should be the best to use in abbreviation of the forum, it will be easier to understand what the person is referring to than using BCT.