The poster looks more WW2 than WW1 to my eyes. This interpretation is supported by the date of this article:
"The Science and Art of Mining: 12th May 1934, Page: 339, Column: 1: Possibilities for Extended Use: The Inspector in Charge of the North Western Division, Mr. W. J. Charlton, describing briefly the "Sylat" prop invented by Mr. Walter Sylvester, says this is a safety prop with the usual wedge to facilitate setting and with means provided for locking the head to the prop. To release the prop all that is necessary is to remove the security pin, insert the hook of the usual five-yards Sylvester chain in the link provided, and give a sharp flick to the chain; sometimes two or more flicks are required, according to the load upon the prop. This operation serves the double purpose of unlocking and withdrawing the head, the load upon the prop assisting. The prop falls in the direction of the drawer, who gives a sharp jerk to the chain if the falling roof threatens to bury the prop. This steel prop will sustain heavy loads, and has the merit of easy withdrawal, as well as easy recovery from wastes, without the operator having to return to the released prop and expose himself under unsupported roof."
http://www.dmm.org.uk/news19/9340512.htm