Affordance and Signifiers
Affordances determine what actions are possible.
Signifiers communicate where the action should take place.
In the physical world, the most common example of affordance is a door. According to this image, Affordances represent the possibility to open the door with the handle. Here gives a clue/sign of what is to be acted upon or in which direction the door should open to “push” or “pull”. That represents the term Signifier.
When the user sees a well-designed(Affordance) door with good perceivable signifiers, the user knows immediately whether need to push or to pull the door, whiteout even having to touch it.
Design with bad affordance, you will notice it immediately and, in some cases, you might get frustrated. Good Affordance with a bad signifier can mislead or not qualify to communicate where or how the action should take place.
Two holes are clearly there to put fingers into. Two holes create a background for an affordance. It makes sense for fingers to be inserted and then the designer gives a clue of possible operations/actions(Big hole suggests several fingers and Small hole, only one). So signifiers that indicate by hole size where the fingers are to go.
Signifier refers to any mark or sound (physical or digital). Signifiers signal things, in particular, what actions are possible and how they should be done. Although some affordance can be visible, others are not but Signifiers must be visible, else they fail to function. If you use the wrong fingers, the scissors still work, although not as comfortable and they fail to function.
So Affordance and Signifiers are fundamentally important principles of good design.
Thank you for reading. ;)