What does the "Constrain Proportions" button resemble in Adobe After Effects?

In Adobe After Effects, the "Constrain Proportions" feature is crucial for maintaining the aspect ratio of layers when resizing them. The button representing this function resembles chain links. This design choice symbolizes the idea of linking two dimensions together, which directly refers to the functionality of keeping width and height proportional during transformations. When this button is activated, adjusting one dimension (either height or width) will automatically adjust the other to maintain the original aspect ratio, preventing distortion of the layer.

The other options, while they may suggest different types of shapes or functions, do not aptly convey the concept of linking or connecting two values that the chain link imagery does. The chain links effectively communicate the idea of a relationship between width and height, making it the most intuitive choice for users.