These signifiers can be in the form of:
Your Characters -Â
Posture, behaviour, expression, response
Costume, make-up
What they are doing
What they aren't doing (that you would expect them to be doing within the context of the situation)
The Location -
Location can be used to echo what a character is feeling internally
Location can be used to contrast with how a character is feeling (sad at a party, happy at a funeral, lonely in a busy street)
Time of Day - Season -
These provide texture and atmosphere (Night = scary, spring = love...etc)
Props -
A dripping tap = tension, irritation, hard-up/unloved etc
A ticking clock/watch = tension, encroaching deadline, boredom
ANYTHING that you see and hear will be read by the audience
That is why you have to be very careful about what is seen and heard, so that the audience don't get confused and mis-understand your intended story.
You will notice that some of the description I used in my Step-Outline is carried forward into the Treatment (in the next section); if something works and is concise/economical, keep it, use it, carry it on and use it in the further development of your script.