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 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.
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.