Sue,
If it were just a service sticker I'd take them off. But the stickers and decals that tell where the machine has come from, or in this case rebuilt by is part of the machines history. So I do leave them if they are not in bad condition.
A machine as old as this one is has a lot of history. We'll never know how many clothes it's sewed, or quilts, or drapery, or what ever else, but with this decal on it, we do know that at some time in it's history it was rebuilt and upgraded, by whom and where.
Joe