According to the UK rule book (
https://www.rssb.co.uk/rgs/rulebooks/GE ... ss%202.pdf" onclick="window.open(this.href);return false;), and simplifying somewhat as there are several pages of this for different types of train:
1. Platform staff must give the ‘station work complete’ or ‘train safety check complete’ signal by raising one arm or a dispatch bat above the head during daylight, or holding a white light steadily at night or during poor visibility.
2. Guard must give the ‘ready-to-start’ signal to the driver by using the bell or buzzer communication. If there is no bell or buzzer communication, s/he must give the
‘ready-to-start’ signal to the driver by displaying a green handsignal (flag or lamp). For a Driver Only train (ie no guard), platform staff must give the ‘ready-to-start’ signal to the driver by displaying a green handsignal or using a right away (RA) indicator.
You'll often see platform staff in Britain using the white dispatch bat. You'll also see the illuminated right away indicator on many platforms. Of course the driver cannot move the train until s/he has authority from the signaller, either a fixed signal at 'proceed' or whatever other method of train control is being used.
In South Africa, the ‘station work complete’ signal is a white flag or lamp, and the 'right away' is a green flag or lamp, although in practice it is often done by radio these days: "Right away, driver!"
The latest rule book I have for Kenya is the 1963 East African Railways and Harbours General Rules. 'Permission to start' is given by the station master to the guard verbally if possible, or by one arm raised high above the head or a white light held steadily above the head. 'Proceed' is given by the guard to the driver by a green flag waved above the head or a green light held steadily above the head. I'm not sure what method is used these days.