WebRestaurant has stainless sheet cake size markers. Mine are plastic and getting old but they are quick and easy to use. If you do a lot of sheet cakes for showers and such and they want the cake marked for individual servings this is the way to go.
they are cool — you only get 60 servings though out of a full sheet 18x26?
I basically get- 88 2 " servings. I lay one down then overlap the grid with the 2nd.
btw we called it scoring
With all the sheet cakes I do, I need one of them. I have just used a long ruler & a toothpick to score. This would be quicker. :))