Try this simple (and subtle) method of signaling to the veterinarian that its time to wrap up an appointment.
When doctors are in an exam room and they have another appointment waiting, an assistant will knock on the door, enter and place a fluorescent green laminated notecard on the counter behind them. If more than one appointment is waiting, the technician will use a fluorescent orange card instead. This is a nondisruptive signal to the doctor to wrap things up, and if they're with a particularly talkative client, they can grab the notecard and say something like, "It looks like I have a phone call from the referral center about a patient. I'm going to go take the call and let the assistant finish up the appointment. Please let her know if you have any more questions.”
We garnered this tip from a veterinary assistant who's now pursuing a DVM degree. You can submit your own tip here.