Masonic Third Degree Symbol
The symbol of the master mason, as it is embroidered on the aprons of Freemasons who have reached the third degree of initiation, consists of a compass, a square ruler, and the letter G. This key image or symbol is what the priests of Kafiristan regard as evidence that Dan and Peachey are not men but gods. The symbol is also present in a hidden part of the temple.
The compass and ruler are tools used in architecture and engineering. Dan and Peachey are engaged in building a modern country and society out of the warring tribes they find in Kafiristan. One of the first things they do is to introduce modern technology in the form of weapons, which ironically are tools more suited for destruction than for building.
Crucifixion
To punish Peachey for pretending to be a god, and for his audacity in attempting to rule Kafiristan, the local people crucify him "between two pine trees." Having wooden pegs driven through his hands and feet, and hanging from those pegs all night, effectively cripples Peachey by rendering his hands and feet almost useless, although it does not kill him.
Peachey appears to view himself as a Christ-like character who brought knowledge and wisdom to unappreciative people and who was crucified by them despite having done them no wrong. In reality, Peachey does plenty of harm: he participates in Dan's mad scheme to take over the area, he subverts the Third Degree, and he is in charge of the army so people fear him.
Crown
Crowns are regarded throughout Europe as symbols of royal authority. In this story, Peachey and Dan set out with the idea of conquering the region of Kafiristan and becoming kings there. Due to a combination of luck and bravado they succeed, although Dan Dravot is the primary ruler whereas Peachey functions more as an assistant. Dan leaves Peachey in charge of one village while he goes on an extended expedition, and returns wearing a gold crown on his head and carrying another for Peachey.
At the end of the story, Peachey has lost his own crown but he shows the narrator Dan's disembodied head still wearing its crown. When the narrator finds the delirious Peachey wandering by the side of the road far from town, he takes him to a hospital where he dies. But Dan's head, and the crown, disappear and are never recovered.
Guns
Dan and Peachey arrive in Kafiristan with twenty "Martini" guns. These appear to be some form of Martini-Henry rifle, which was a breech-loading single-shot gun issued to regular troops in the British army from 1871 until after World War I.
At the time this novella was published (1888), Martini rifles and the specialized ammunition they required were state of the art military equipment that could not possibly have been obtained by legal means in the Indian subcontinent. They were being copied, according to the text, by artisans in Kabul. Later, after Dan and Peachey establish themselves as rulers, Peachey goes on a mission to buy a hundred more of these imitation rifles and some more ammunition.
Although the Masonic symbol is used to represent a form of spiritual or intellectual authority and the crown represents legal or political authority, in this story the guns are what represent actual raw, physical power. Once Dan and Peachey teach the locals how to shoot and arm them with state of the art technology, they are no longer in control of the country and are deposed as soon as their subjects realize they are not gods and therefore not fit to rule.
