The Royal Ordnance Factories and Depots were vast sites employing many hundreds or thousands of workers. In the days before computerisation, keeping a tally of which staff were on or off site was not easy and relied on manual methods. Whilst clocking in cards recorded when a person arrived and left, in the case of an emergency checking through thousands of cards was not an efficient way of seeing who was on the premises. One common method of tracking staff in use before the computer age was the use of metal tallies. Every worker was assigned a metal tally with a number on it and these were handed in before entering part of a factory and hung up on a peg board. This then allowed a foreman to know precisely how many people, and who, was in a section. This was particularly important in hazardous industries such as coal mining and explosives, such as the Royal Ordnance Depots. Today we have a pair of such tallies form the Royal Ordnance Depot Didcot:
The two tallies are of different designs, although both have ‘RAOD Didcot’ marked on them. One is numbered 2566:
Whilst the other has an ‘A’ prefix and is number 1018:
The use of the A prefix suggests that they had used up all the numbers up to 9999 and so had to start the sequence again. In 1918 the Nottingham Evening Post reported on one ordnance worker who had been prosecuted for fraudulently using a metal pass disc:
THE WRONG PASS – MUNITION LABOURER’S FOOLISH CONDUCT
For attempting to enter a munition factory with an unauthorised disc or pass, a labourer named James Dunn, aged 50, was fined 21s. at a Midland police-court today.
Defendant, who was a discharged soldier, had lost his own pass, but instead of reporting it to the management he tried to get in with another disc. The danger of such a proceeding is that discs which are lost may get into undesirable hands.
Defendant’s further explanation was the substituted disc was given him by his wife, and that it had belonged to a lodger.
For further information on the use of tokens by munitions workers, please check out this excellent website.
Tales from the Supply Depot 
This is similar in concept to the tokens used to get tools from stores in some facilities. You had to hand in a token to be issued the item and it was given back to you on return of the tool.
We used tool tags plus signing the kits or shop boards in and out and also used cards with our pictures on them to move ‘in’ or ‘out’ if you worked there or area passes/ID cards were left at the gate if you didn’t, when entering the bomb dump so we knew who was inside if something happened. It was a BIG no-no to not move your card or let someone in without leaving an ID.
( unless you were picking up or dropping off a weapons convoy after hours 😉 )