When you're playing Splendor, according to the instructions, the youngest player goes first. Of course, just to keep things interesting, it's always nice to swap the starting player around. This special token indicates where the game ends based on the starting player so nobody has to think about it during game play.

The height is equivalent to two chip thicknesses so that it fills that empty gap on top of the pile of 5 gold coins so that it's the same height as the 7-chip piles in the box. What box, you say? Why, the Super Compact Splendor Holder of course:

http://www.thingiverse.com/thing:1055379

I painted mine shiny gold so as to easily distinguish it from in-play coins.

If you found this useful, please share your work and be sure to peruse my other submissions which are almost as varied as they are many:

http://www.thingiverse.com/3E8/designs

Enjoy!

July 20th, 2016 update: Rotated the arrow such that it actually points at the final player. In the images, it's pointing at player 2 (assuming a 4 player game).

Sept 13th, 2016 update: Can't believe I got the turn order reversed! I checked the instructions, and it's clockwise.... so I've updated the file with the arrow pointing at the actual player who ends the game. :P