I took a look at Billboard's hot pop, country, rock, and hip-hop charts to see how frequently artists had filed US federal trademark applications for their individual names or band names, and to see how broadly artists tend to file. This is a very narrow dataset, with just eighty artists or bands, but it still provided some interesting information.
The three main classes for which artists sought protection were no surprise. Class 41 (live performances, etc.) were the most commonly protected, followed by Class 9 (digital recordings and/or CDs) and Class 25 (clothing) in basically equal measure. Classes 16 (paper products like posters), 18 (bags), and 3 (perfumes, etc.) were the most common merchandising classes after clothing.
Hip-hop / R&B acts were the most likely to file for at least the music-related classes, although pop acts tended to file for slightly more ancillary "merchandising" classes. Country acts lagged a bit behind, with rock acts tailing by a fairly considerable margin.
Data on my findings follows! I will replace the chart below, a png screen-capture from Excel, with a nicer Google Visualizations chart as soon as I figure out how to rig Wix to allow me to do so.