As an actual USPS city carrier, I guess I should weigh in!

First off, there is an actual registered USPS tartan (shown below). Why it was created, and whether or not it's been "officially" adopted by the USPS, I have no idea. Obviously not for carrier uniform purposes! And, I'm pretty sure we don't have our own pipe band!! So, the tartan is a bit of a mystery....

Personally, I don't have much of an interest in wearing a kilt for work, because I have a driving route and would just be crushing my pleats all day. However, I do think the postal blue utilikilt-type garment in a durable fabric would be a reasonable and comfortable alternative to the carrier's "walking shorts" in warm weather. It would not detract from a "professional" appearance any more than the shorts do. The exact same scrawny or fat or hairy or scarred or tattooed or grubby knees and legs would be on display!

But, the idea was shot down and it doesn't distress or surprise me. Our unions, postal management, and their mindsets and relations with each other are stuck in the 1890's anyways....