The Operator Symbol

The Operator Symbol is a circle with an "X" drawn through it: ⨂. It has been revealed that the original idea was for it to mean 'No face' by Jay. It has a connection to totheark, as they made MarbleHornets aware of it being named 'Operator'. The encircled X is a real life math Operator. It was first depicted within the MarbleHornets series and has since appeared in many other Slender Man series as well, including TribeTwelve and DarkHarvest00.

Since it was used in MarbleHornets, its popularity has led it to be synonymous with Slender Man by the online community, despite Marble Hornets stating The Operator to be a seperate entity from Slender Man.

Speculation

There are a number of theories surrounding the Operator Symbol's function.

Function

The symbol summons the Operator to wherever it is drawn.
The symbol acts as a ward against the Operator to keep him away.
The symbol acts as a warning sign against the Operator.
The more the symbol is drawn, the more influence the Operator has in the area or on a person.
The symbol is perceived to the Operator as a large eye, or observing device and he is drawn to it.
The Operator symbol can also be a possible portal for the Operator.
The symbol, wherever it's drawn, means that the Operator is near the area.
The symbol may be, in fact, a rune much like The Rune of Severance and act as a means to control something such as a human being, account or object. As well as possibly being a rune for the number zero.
The symbol may have no function itself but acts according to the beliefs of the person viewing it.

Real-world meaning

An encircled "X" can denote a variety of ideas in the real world. For instance, in data modeling, the encircled X denotes the exclusion principle between two populations.^[1] In mathematics, the circled X is a mathematics operator meaning "circled times,"^[2]^[3] and describes the tensor product of two vectors.^[4] Another version exists as a circle with a superimposed X,^[5] and is used to describe the three-dimensional directionality of an arrow.^[6] Other versions of this symbol include a circumflex accent,^[7] and within a double circle.^[8] Non-mathematically, the circled X, or heavy circled satire,^[9] denotes the location of a police station on Japanese maps.^[10]

However, the circled X has also darker meanings. For instance, the symbol was marked on Ellis Island immigrants to denote insanity.^[11]^[12] Samuel Clemens, also known as Mark Twain, used the symbol (the escutcheon in his diction) in his notes to represent a skull and crossbones.^[13] A circled + was used by the Zodiac Killer in his letters to police, which is strikingly similar to the Operator Symbol. The encircled 'X" is also similar to Cornelius Agrippa's Planetary Seal of Jupiter, based upon Kamea numerology of the Hebrew alphabet.^[14]

No substantial connection has been shown between any of these common encircled X symbols and the Operator symbol associated with Slender Man.

Trivia

The Operator Symbol also appeared in the IOS game Slender Rising 2 in the form of a portal the player must get to after collecting the seventh sign or saved the seventh lost soul in order to escape. Also in both Slender Rising games, the letter O on the signs is replaced by this symbol.
The only known canon appearance of the Operator Symbol is as the loading icon on the loading screen of Slender: The Arrival.