We have had several occasions for calling a sudden halt to events in our services, and the obvious way to do so was to use something like the STOP sign familiar on New Zealand roads. It happened that on the first such occasion we also wanted a corresponding GO sign, so we constructed a double-sided version in the obvious way.
There is nothing particularly clever about it. Perhaps the main feature is its rather sturdy construction, intended mainly to ensure that the sign didn't fall apart when rotated fairly briskly to show alternately STOP and GO signals. The diagram below illustrates our design. It was about 70cm across and mounted on a 1.5m stick. The yellow, pink, and purple bits are wood. ( The colours have no significance; they are intended only to identify the parts in the two views. )
The signs themselves were made of paper ( for the visible bits ) wrapped round a thin hardboard octagon. There are three layers of paper : white for the background, red or green for the main colour, and white again for the characters. There are glued together.
( Click either picture for a separate version. )
We used this sign in two of our services :