The 24th Warwickshire (Birmingham) Battalion's area of responsibility was, I believe, Moseley. Each Company (obviously five at least) would have had a defined geographical area to look after and that would in turn have been split down further to represent the patch of particular platoons, one of which this picture shows. Note the older men, several wearing Great War ribbons: survivors of the Western Front and elsewhere, taking up arms again little more than 20 years after coming home from the war to end all wars.
The 24th, just one of some 47 in the county and 26 in Birmingham itself, appears to have been a bigger Battalion than most and included more than 70 officers in 1941. This would mean that the unit as a whole would have had a membership of well over 1000 blokes (and, later on, a number of women). The population would have changed a bit as the years went by, with the younger fellows being called up and a few dropping out due to age or ill-health. But many would have served for the entire period, from the middle of 1940 until stand-down in December 1944, a record of remarkable, devoted and entirely voluntary service.
Chris