1
The witch flew on a broom.
To express this classic Halloween imagery, you would sign 'witch' followed by the signs for 'fly' and 'broom'. You can use your facial expressions to show how fast or high she is flying.
2
She dressed up as a witch for Halloween.
For this sentence, you would start by establishing the context with 'Halloween', then sign 'she', 'costume' (or 'dress up'), and finish with the sign for 'witch'.
3
I watched a scary movie about a witch.
To explain the plot of the film, you would sign 'movie', 'scary', 'watch', and then 'witch'. Make sure to use a frightened facial expression when signing 'scary'!