It's possible people might never notice HRT changes. Growing out your hair will get you noticed, though that's an avoidable problem... breast growth might be a problem within six months if you're lucky, but if you're not, breast growth may never be difficult to hide.
Other than those two, people won't notice enough change to come to the conclusion that you're transitioning. They might shrug the rest off as strange, or may not notice at all.
Facial changes are a bit borderline; sometimes they're significant, sometimes they're not. Even if they are, though, people may or may not notice, because no matter how much change happens due to hormones, facial features will change only subtlely, at best. When they notice, it's because they realize what those subtle changes have actually done with your face - and people that are that observant about oneself are quite uncommon.