Sure, they will taste the same without it, but if you hand someone a roll with a perfectly rounded top, with no classic five-spoked swirl, and tell them it’s a Kaiser Roll, you’ll just get a funny look.
Classically, the look is made by folding up the dough. Some people, though, find this too time consuming, or can’t get it right — the folds come apart on them during rising and baking, and the roll ends up looking like a mutant starfish.
A Kaiser Roll stamp provides perfect, uniform-looking Kaiser Rolls with the swirl on top, though any purist won’t be fooled for a second into thinking the dough was actually folded.
The stamps are made of plastic or metal, and will be anywhere from 2 1/2 to 4 inches (6 to 10 cm) wide. They are flat discs with a handle on one side, and on the other side dull, protuding “blades” in a 5-arm swirl pattern (though occassionally a stamp with a more general swirl pattern may be seen sold as a Kaiser Stamp.)
When you have shaped your rounds as a round piece of dough, before the final rise, you press the “bladed” side into the top of the roll to form the pattern. When risen and baked, it will have the classic Kaiser Roll pattern.
Make the pattern the old-fashioned way (see Kaiser Rolls), or cut the pattern in with the tip of a sharp utility knife.