We've been to Alaska a couple times. The first time, our guide gave us some tips about looking out for bears. Alaska has two kinds of bears, black bears which are the smaller and less aggressive of the two and brown bears, also known as grizzlies, which are larger and more aggressive. When hiking, the guide said to make a lot of noise, dress in bright colored clothing for visibility and carry pepper spray. She said most bears do not want to have contact with humans, and if they hear or see you, will often run the other way. To prevent stumbling upon a bear, she also said to look for bear signs such as scratches on trees, as well as bear scat. You can tell the type of bear by it's scat: black bears have a diet that is mainly berries and fruit, and their scat is small and will contain bits of twigs. Brown bears on the other hand have larger scat and it will contain pieces of bright clothing and smell like pepper spray.