A fabulous skull and crossbones fob wax seal pendant … the skull above crossbones is surrounded by the crown jewels: the crown, royal scepter, orb and the sentiment MEMENTO MORI.  I've made this replica pendant from an original antique seal in my collection and it dates back to the Georgian era, the mid 18th century, 1750 of earlier based on historic waxes found that were impressed with this seal and I found another impressed red wax example from 1759, shown in photos. 
There’s an historical figure on the back side of the seal pendant … I am not sure who this mystery man in profile is, but wonder if it might be King George II.
The original fob seal was part of a museum collection and the side with the profile is numbered in white ?829? … I’m not sure if the first number is actually a 3 or an 8 as it’s a bit worn.

- approximate height -1 1/8“ (30mm)

- matrix measurement - 3/4” x 5/8” (18mm x 15mm)

- pendant thickness - 1/8" (4mm)
- wax seal charm metal - sterling silver (.925 silver)
*** charm only - cable chain sold separately here
- and the watch chain style chain is available here
- photographed with a US dime and inch ruler for scale

I've made a mold of the original memento mori antique seal and cast it in sterling silver. I've included photos with the original antique steel seal.

A little bit of history ...
It's likely that this seal commemorates a member of the royal family, quite likely one in the Stuart Monarchy. The St. Edward's Crown, along with the orb and sceptre, are three authoritative symbols of the monarchy and used at the coronation of each new sovereign. This seal may represent the Crown Jewels which are kept at the Tower of London in the Jewel House. 
However, this seal may represent parts of the Honours of Scotland, or Scotland's Crown Jewels with the jeweled crown, sceptre, and the sword of state.  These national treasures were used for Scottish coronations and they are now on display at Edinburgh Castle after famously hidden for a century before their rediscovery by Sir Walter Scott in 1818. They date back to the 15th - 16th centuries.   

Impressed with history!