The Operator (Slenderman) Symbol

The Operator Symbol is a circle with an "X" drawn through it: Ⓧ. It has not been revealed what it represents or what its function is except that it is somehow connected to the Slender Man. It was first depicted within the MarbleHornets series and has since appeared in many other slender series as well. It has appeared in MarbleHornets as well as TribeTwelve
Since it was used in Marble Hornets, its popularity has led it to be synonymous with Slenderman by the general online community.

Speculation
There are a number of theories surrounding the Operator Symbol's meaning and function, however one should still keep in mind it is used in ARG's and not in any actual Slenderman lore, thus utilization of any of these things will net no results in reality.

Meaning

It may represent the Operator's face, because the Operator has no face.
It may represent the Operator's eyes, as seen in MH Entry 50 and in Forecast.

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 Operater is near the area.
• The symbol may have no function in itself but act 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. In mathematics, the circled X is a mathematics operator meaning "circled times," and describes the tensor product of two vectors. Another version exists as a circle with a superimposed X, and is used to describe the three-dimensional directionality of an arrow.Other versions of this symbol include a circumflex accent, and within a double circle. Non-mathematically, the circled X, or heavy circled satire, denotes the location of a police station on Japanese maps.

However, the circled X has also darker meanings. For instance, the symbol was marked on Ellis Island immigrants to denote insanity. Samuel Clemens, also known as Mark Twain, used the symbol (the escutcheon in his diction) in his notes to represent a skull and crossbones. The encircled 'X" is also similar to Cornelius Agrippa's Planetary Seal of Jupiter, based upon Kamea numerology of the Hebrew alphabet.

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