Both men and women make the mistake of letting the logo wear them rather than the other way around. The theory is that by showing off a huge, designer logo, you're showing the world that you can afford to wear said designer's clothes. Besides this being bad manners by bragging, it's usually just plain bad. If a prominent designer emblem looks like it might be too much of a good thing, tone it down or you'll end up looking more like a billboard than a style-savvy man about town.
Choose your pieces to showcase one or two quality items, and go for a flattering cut instead of a popular brand name. If you're wondering about the advisability of buying a shirt or other garment with a prominent logo, ask yourself this question: Is the designer going to give you a rebate for the free advertising? If not, then go for something that shows off your best assets, regardless of who designed it.
The same can be said for jewelry. You don't need to wear a diamond-encrused Mercedes symbol around your neck to show everyone how much money you have. Understated class is much more appealing.