 In some forces different types of staff (paid ('regular') police officers, special constables, PCSOs and other police staff) are assigned different ranges of numbers, so a person's role can be deduced from the number, but these systems are force specific and there is no national standard.For the letters shown on riot helmets and the roofs of police vehicles, see Home Office radio callsigns.In France, the wearing of the collar number is compulsory, save a few exceptions, from 1 January 2014.