The 27 will have a checkered rib and top strap. They will be plain matte on a 28 no checkering.
Howdy again
There really is no mistaking a Model 27 and a Model 28, if one gets a chance to handle them.
This photo shows the top of a Model 28 at the top and a Model 27 at the bottom. As stated, the Model 27 has checkering on the top strap, the barrel rib, and even on the tang of the rear sight. These features are a carry over from the Registered Magnums, that were the fanciest revolvers S&W was making in the 1930s. Also, with the exception of the Model 28, almost all modern S&W revolvers have longitudinal grooves on the tang of the rear sight.
Another view of the top of a Model 27 at the bottom of this photo. Notice the checkering extends the length of the barrel rib and up onto the rear sight base. The revolver at the top of this photo is a Model 19-3. Notice the longitudinal grooves on the tang of the rear sight of the Model 19, typical of almost all S&W revolvers except the Model 28.
Regarding the finish of the Model 28. It is often described as being a matte finish. Clearly not as highly polished as the finish on most S&W revolvers, the Standard Catalog of Smith and Wesson lists the finish on a Model 28 as 'satin blue finish'. In fact, over the years the amount of polish on Model 28s varied. Sometimes it was almost a matte finish like a Victory Model, sometimes it was almost as highly polished as any other S&W revolver.
This is a photo of a Model 27 that left the factory in 1959.
A Model 28-2 that left the factory about 1964. Both photos were taken outdoors in the same spot. But they were taken on separate days, so the lighting is not exactly the same. This photo was taken in slightly stronger light, as evidenced by the shadow of the revolver. The photo of the Model 27 was taken on a cloudy day, so the light is more diffuse. Still, it can be seen that the finish of the Model 27 is more lustrous than the finish of the Model 28. However this Model 28 does not have a 'matte' finish. A matte finish means the finish is dull with no reflection at all. Clearly, this Model 28 has some luster, particularly on the cylinder. Also, notice the different front sights. The Model 27 has a Patridge front sight, the Model 28 has a Baughman Quick Draw front sight. The white paint filling the marking on the barrel of this Model 28 is not typical, it was done by a previous owner.