For Brownies, the challenge was Semaphore, and as it was a task for the older Brownies in a unit, a lot of 'semaphore games' were invented so the unit could provide the older girls practice at using Semaphore 'for real', whilst also encouraging the younger girls to look forward to their turn at learning the magic secret code.
The most common learning method, was for girls to learn the 'first circle' initially - the letters from A to G, where only the right hand moved. They could then practice signalling words which used just those letters, e.g. bag, cab, fad, bed, etc. This also helped them with learning which hand was used for all of these letters, as Brownies often find difficulty with left and right. They could then learn the 'second circle' and add H, I, K, L, M, and N to their repertoire, allowing a wider range of words. After that there was the 'third circle' - O, P, Q, R and S, the 'fourth circle' T, U, and Y, and then the randoms, J, V, W, X, and Z.
Once there was a girl or two in each Six who could read some of the letters, races which involved the Leaders sending instructions by semaphore could be used, it could be used as a code for treasure trails, and there was handicraft in making flags to signal with, in two colours.
For Guides, the challenge was learning Morse. There were a range of different techniques suggested for doing this. One was to start with the 'dots' - E, I, S, H - and the 'dashes' - T, M, O. Then the 'opposites' - A, B, D, F, G, Q, N, V, U, L, W, Y. Then the 'sandwiches' - K, F, R, X. And 'the rest' - C, J, Z.
Others suggested inventing phrases to incorporate long and short syllables which matched the signals, which could be memorised. So terms like A-Broad, Broad and-nar-row, Cheeky Charlie, Dou-ble up, etc.
Once learned, Morse could be signalled by radio by using a buzzer set, using a whistle, tapping on a hard surface or playing a musical instrument. But it could also be signalled by light - by long and short flashes of a torch, or by a signalling lamp.