Many bikers do more than just ride their motorcycles? they make biking into a serious hobby. In addition to buying up anything they can find to make their motorcycle look amazing and run better, they also buy various merchandise related to biking and collect biker memorabilia. While not all bikers go crazy and have an entire room dedicated to their motorcycle memorabilia collection, some do. There are many different items out there that might interest you. Some are made for the general biker who occasionally buys something bike-related, while others are aimed at the hard-core collector.
T-shirts, for example, are all over the place. You'll find shirts with generic motorcycles on them, some with biker sayings written on the front and the back, and some with the logos of specific brands. You can bet that every biker owns at least one of these shirts. Many times, bikers get motorcycle-related t-shirts as gifts because they're an easy option. Bikers who collect t-shirts and other usable items are more casual collectors.
Then there are the mid-level collectors. These guys don't buy everything motorcycle-related, but they do have a good sized collections of things they really like. Some, for example, collect motorcycle patches. They wear their favorites on their riding gear, but the rest they either display in frames or use to decorate other items, like cloth shopping bags, throw pillows, and even their baby's clothing. But they don't buy expensive items aimed at only collectors.
No, those pieces are usually purchased by the hard-core collectors. These guys buy just about anything related to bikes or to their particular brand. The hard-core collector is the one with the Harley-Davidson motorcycle telephone, the motorcycle replicas, and just about anything else related to bikes. Most of them focus on one particular brand, and they go all-out.