Ariel, it is not a strict uniform, just the local costume.
![Wink](images/smilies/wink.gif)
And not specific to zeybeks either. This is mostly similar to most town folk wore in Ottoman Anatolia and Balkans in 19th century.
And that so-called "Zeybek" yatagan with T shaped ears. That is not specific to zeybeks either. It is just easier to make than a real ear shaped handle. And in late 19th century-early 20th century small town blacksmiths were not expert swordsmiths like in earlier times, so most made those ears T shaped because it was easier to make. Some yatagans that were made earlier also got those T shaped pommels when their original fancy handles got fallen apart and their owners or the local knifesmith made these simple handles for them.
Zeybek yatagan is just a name given by contemporary antique dealers, just to make it easier to classify and make it sound more important.