Sometimes, people need more than a hint to get the point across. My own example- I've visited the same bank every week for the past 4 years, and there are two main tellers that always recognize me, and carry small talk with. When I started presenting full time, one of them picked up on it immediately. The other, though, would see me from a distance and call me over as "ma'am," only to immediately apologize, and switch back to male pronouns. I was caught off guard (as I'm sure you are, in your situation), and didn't correct him at first. I finally told him, and it hasn't been an issue since.
It doesn't have to be a big deal- they're people you've made casual rapport with, and probably see fairly regularly, but it doesn't have to be a big coming out. Just give them a casual "oh, it's actually 'she'," and they should get the idea. I think they're just used to how you presented over the years, and especially if their behavior hasn't changed negatively towards you to this point, just that nonchalant pronoun correction could be enough.
You look fem in your profile pic. I don't imagine the switch will be very hard for them once they've put the pieces together 🙂