he might use them as labels to remind him which key changes his sounds
sometimes it's too hard to switch patches and sounds while performing, so you can preset them to individual keys
wtf... I never noticed that when i saw them last year, and i was like 2 feet in front of him.. hmm, the show is on the 18th over here, so I will play close attention to that.. I also play the synth and most of bodom's synth riffs can be done with one hand... but not all of course...