It is rare that something I try just works but this is something that was simple and helped one of my teams.
We were finding it awkward to track the overall state of a story on our manual board. Without this it was easy to miss something interesting during the stand up and even more difficult for the business to look at the board and understand what we were working on.
The team always talked about 'bringing an item into play' so I started to use a CD/DVD play symbol to indicate the items we were currently working on. This quickly evolved to use the stop symbol to show a story had not been started yet, a pause symbol to show the story had something blocking it and eventually a fast forward symbol to indicate that the team were swarming on that single story. Once we used the eject symbol when a story was pulled from the sprint due to a really late change in customer requirements.
It seems almost trivial, but the mere fact we could see the state of all the stories on the board helped with:
1) WIP - before it was too easy to start working on something without finishing something else. There were several instances where we had a high WIP and some items could not be done by the end of the sprint. Being able to see status of the board pretty much stopped this overnight. Never quite understood why but the added visibility meant it was much more difficult to hide opening another story, allowing the team to form and keep an agreement on WIP.
2) Stand ups - we focus the stand up on the 'in play' stories, drilling into each one and organising the day around closing them. We often update the symbols to reflect what we agree to do for the day e.g. pausing a story so we can swarm on another one if we feel it is stuck and we won't incur waste in doing so.
3) Waste - the states of the story give clues to any waste that might be happening during development. If a story is paused - do we have a delay or hand-off? If a story is in play but seems to be stuck in a particular phase of development - maybe we have re-learning happening? If we have to play a paused story - maybe we should be looking for task switching? I can ask questions that help the team see waste and record it more accurately but the clue's start with status of the story.
We have also used padlocks to indicate if something should not be touched - happens occasionally if we are working on anything that needs approval by the organisation but we are slightly ahead of the curve and have already planned the item.
The key observation is that everyone 'gets' these symbols. They convey specific information quickly and easily with no training required. They drive team conversations and most importantly, the team has adopted them which is probably the best endorsement you can get.