It would depend on the shirt, but generally I avoid graphic/print on them. It might be fun to have a trans shirt, but I think I'll wait until I'm more confident in my passability to wear such a thing outside - provided the shirt works in an outfit anyway.
I'm not really out, but I don't make any special effort to hide my trans status either. Proud, for sure, but I don't really feel like everyone needs to know. It'd probably be more effort than it's worth.