What does the mark FI 14kt mean?

The 14kt refers to the gold - 14 karat gold.

The FI is a color-grading scale based on the color of the stone, usually a diamond. The scale that utilizes FI is the GIA Scale or Gemological Institute of America's Scale.

Using the information below, you can determine that FI means the diamond is colorless to near-colorless.

D, E and F = Colorless

G, H, I and J = Near Colorless

K, L and M = Faint yellow

N, O, P, Q and R = Very Light Yellow

S, T, U, V, W, X, Y AND Z = Light Yellow