A feather in your cap
Definition 1 of 1
Pro Tip 1/3Positive Connotation
The phrase is used to express a sense of achievement and pride, similar to displaying a trophy. 
After years of hard work, getting that promotion was a feather in your cap.
Pro Tip 2/3Metaphoric Origin
Historically, warriors added feathers to their hats for each victory, representing success. 
Securing the deal with the client felt like adding a feather in your cap.
Pro Tip 3/3Casual Use
Best used in informal or colloquial settings, rather than in very formal or academic writing. 
Completing the marathon was a real feather in your cap, wasn't it?