That very brief description of the sight hints at a King mirror sight. We really need more information and pictures, a King Equipped 357 Magnum could fall into the run of Registered Magnums which can be VERY high dollar revolvers.
For now just ignore the John French logo, he may have been the original owner or the gun may have been a Gunsmiths special with John French being the name of the gunsmith.
What you should be looking for.
First the makers logo and manufacturing location. The 357 Magnum is a post 1935 caliber and this gun should have some manufacturers information stamped on it somewhere. On a Smith & Wesson the logo will be on the frame behind the cylinder on either side above the grips. S&W will also have Made in USA and the manufacturing location stamped on the right side under the cylinder.
Second, the serial number including any letters proceeding the serial number. This may be repeated in multiple locations, such as under or on top of the barrel, on the cylinder, on the crane, and under the grips on the grip frame. BTW, you may also find assembly numbers which are not serial numbers, they are tracking numbers to keep the fitted parts together during the manufacturing process and are generaly hand stamped with poor alignment where serial numbers will normally be well aligned, spaced, and stamped in one strike.
Finally, good sharp pictures take with a decent digital camera. This site does feature the ability to upload photographs to the site so an image hosting service isn't required, go advanced and select "attach Images" and upload them from your computer. However, when uploading images to the site resize them to 800x600 pixels or smaller, hint size to 800 x 600 and save in JPG so they will be large enough to see well.
