Watermarks
Single line letters
Double line letters
Between 1895 and 1916 the U.S. government used two different watermarks, double line and single line with the letters "USPS".
By placing the watermark face down on a dark surface or holding it up to bright light you might be able to see the watermark. If on the 1895 to 1916 stamp you cannot see the watermark it might be a good idea to invest in Watermark fluid and a watermark tray (examples are shown later). Ronsons lighter fluid works just as well as watermark fluid. Both fluids evaporate quickly.
Put enough fluid in the bottom of the tray, lay the stamp face down. In a few seconds the stamp will absorb the fluid and reveal the watermark to you.
As you will see from the illustrations the letters can span several stamps, so on the watermark, for instance, you can see only part of the letter S in one corner and only part the letter P in the other corner.
