Unique icons represent unique functions or features. The downside to using them is that they can be hard for first-time users to figure out. If you use them, make sure that you include text labels so users don’t have to decipher their meanings.

Logo icons would be one example of unique icons. The Sketch logo is a stylized diamond. For someone unfamiliar with the program, the diamond will be meaningless. But for those who have used the product, it’s immediately recognizable. Keep that kind of impact in mind when using unique icons.