A quick guide that will show you how to enable Playstation button prompts if you are using a DS4 controller.
Guide to Playstation Button Prompts on DS4 Controller PC
Step 1: Open Big PIcture Mode
This can be done by clicking on the rectangular box in the top right corner of your Steam client.
Step 2: Click on Settings
The cog, 3rd icon.
Step 3: Click on Controller Settings
Step 4: Untick "PlayStation Configuration Support"
Unticking "Xbox Configuration Support" is optional, as I've found that it does not matter if you're using a DS4 controller.
Step 5: Finished
Now PlayStation button prompts should be shown in your game.