You have the 50c Jefferson from the years 1894-1903. It is comparatively scarce.

To know which page you need to look at for the value of the stamp one needs watermark fluid or lighter fluid (both of these are extremely flammable and should be used with extreme caution, outside, in a safe area far away from combustible materials). Soak the stamp in the fluid in small plate with a black or very dark color. The watermark will show, sometimes faintly by looking at the back of the stamp. The watermark fluid will quickly evaporate from the stamp, leaving the stamp and its gum intact. If there is no watermark on the stamp then you can value the stamp by clicking here.

If the watermark has part or all of the letter U, S or P, as shown above, then you can value the stamp by clicking here.