This is the semaphore alphabet:

 

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Image by kind permission of http://scoutnet.org.uk/

 

 

Someone at the top of the hill sends a message to a friend in the valley. A person in the valley behind also sees the message being sent. They get the same message. What is it?

Are there any words that can make sense when viewed from the front and the back? We have found at least one!

 

(Dave wrote to say that in reality, at the beginning of every message the sender should send 'J', which is also the direction sign. This way the receiver knows which way round the message is and so can translate it correctly from front view or back view. Thank you, Dave.)