This indication is more rare than some of the others, but it is important. It effects the sound, the volume, and provides a neat visual effect. Do not assume that you are already doing this if you play off the leg. Bells up indicates a more pronounced lifting of the horn, usually to a position nearly parallel with the ground. It is important for the audience to see the bell flash. It is also important for the horn player to your right to see the conductor, so make sure you are sitting far enough apart that you don't put your bell right in their face. It is also considered polite NOT to point your bell directly into the ear of the player next to you, so resist the temptation no matter how many notes he's missing.