I attach my bells to the stem on both my bikes with drop bars. Brass bells now.
On my bike page, you can see where I attach it on my blue Rambouillet- in the pix with the grocery panniers:
http://harmonias.com/bikes/

Since those pix were taken, I got two nicer brass bells and have them on both my bikes now. Love having bells, and I find them very useful.
When you place them, you have to adjust how your thumb will hit the ringer lever just right. My husband got a black hose clamp to attach the bell around the thicker stem, and we used a little patch of bike inner tube to protect the finish of the bike where we clamped it. The rubber also keeps the bell firmly in place.