Exceptions to that rule include: 1) early 1900s models that bear only the American Standard or Wadsorth name, and 2) some late 1970s LCD/LED models that bear only a Swiss maker's name or symbol or no case signature at all. With just a couple of easily recognized exceptions, a genuine Bulova watch will bear the Bulova signature somewhere on the back of the case, either on the inside or the outside, or both.
For the vast majority of Bulova watches, no case manufacturer signature other than Bulova's appears anywhere on the case, and every genuine Bulova watch bears one of the known Bulova case signatures-of which there were many more than you might think.