Diablo II Rune Words - Can you make Call to Arms using a Five Socketed Bow
According to Diablo wiki it works for "All Ranged & Melee Weapons." So yes, you can put it in a bow if you really wanted to, but I would highly recommend finding a 1 handed weapon to put it in as the bow is a 2 handed weapon and will limit you from potentially dual wielding it with another + skill weapon in the future for even better war cries.
And as an additional confirmation, here is a screen shot of call to arms in a bow:
