The brand is usually designated on the outside of the jeans in various ways. For instance, you can usually tell designer jeans by the stitching on the back pockets. There is also usually some piece of leather or cloth with a logo and or name on it. Sometimes, Diesel and Citizen both do this, there are little tiny pieces of cloth in places, if you look you can tell the branding. Sevens are easy to spot because of the maroon and gold label on the back pockets. Once you've worn designer jeans you won't want to go back; my Citizens are way more comfortable than my H&M jeans or any other non-designer brand I've owned for that matter. The denim is softer and holds its color through more washes, and they way the seams are stitched, you can barely tell they are there. On that note, I also don't pay ridiculous prices for my jeans; I've never payed more than $60 and I usually get out for less than that.
Just got a pair of AG (Adriano Goldschmied) jeans today for $32; I'm liking them so far, they seem to be on par with Citizens and Sevens.
I am an older person, so like most of my peers, I can only easily put jeans into two groups, levi's with their little red, but visible tag, and all the others, I think expensive, with the stitching with some shape, like a cursive "h", or something, and all the knockoff companies of those higher end ones which look the same to me.
But there is no way in the world I can tell you the difference between a lucky, nudie, habitat, paper/demim, and any other from another. And when Hollister or AE, or AF make a similar looking jean, there's no way I can tell outside of me simply knowing they are not Levi's. I don't think my middle age demographic shops that much at Lucky's. A new Lucky's store opened in my town's mall and it's staffed with young people and I am by far the oldest person I have ever seen in that popular store. Jeans to my demographic still seem pretty generic unless I have a kid who is way into the minute differences between designer jeans stitching patterns.
When I was younger (teens/20s), the big "in" thing outside of the standard Levi's were the similar alternatives like Lee and Wrangler, and the high priced ones like Vanderbilt. Today, there are so many high end ones, it's mind boggling.
And yes, at least for me, the only way I can tell the designer ones and get any idea is looking inside at the tags, and looking at the price tag.
This may sound weird, but one way besides checking out the clothes, to tell how good a product is, is that I check out the tags on the inside. Ecko clothes, which I love, have serious "taggage" on the inside, and if a company pays that much attention to their tags, they probably do so with their clothes. I have had Ecko stuff for years and I am still yet to have one fall apart on me. What's weird is that one day my wife bought an Ecko cap for me, not looking at the clothes, and neither of us knew that it had anything to do with young people or rap music. It was just on the shelves near Nautica and Polo stuff.
Of course, these days, I can't afford anything Ecko, but I still admire their quality and extreme durability.