Unicode is a fact of programing life; in Prolog one can parse by specifying any combination of characters as xf, xfy, or fy with a precedence metric from 0 to 1000.

But like C#, F# has no recognition of Unicode symbols as operators (classifying them all as +-precedence xfy would be better than nothing; parentheses used to be quite common in functional languages). However, both permit certain Unicode letters as identifiers.

So whether it's to clarify a mathematical algorithm or just for fun with friends, here are the Unicodes that are accepted in identifiers along with some thoughtful and thoughtless ideas of what they mean. Here's the most interesting I could find out of tens of thousands of characters (Yeah my imagination flails at the semiotics of Mandarin Chinese).

Science:
Σ summation or another aggregation operator e.g. build a list of values
Π pi; Π2 is 2*pi;
ǂ not equal
ƒ a function
Δ Change or minimum action resolving constraints
º temperature (ºf or ºc)
θ an angle measured in radians; in particle effects: metric of an angular spring

Øø null set
Λ the intersection of two sets
γ the union of two sets
º angle measured in degrees or else temperature (ºf or ºc)
Ɨ an element not included in a set
ω angular momentum; in people, spin;
Ϯ student's t-test; probability that a coin tossed N times is unfair assuming maxint prior 0.5
ε existential quantification
Γ for all or universal qunatification

Programming (some practical, some just for fun, but I defer all F#-domain interpretations to its developers):
ν a vector in rθ or xy notation with possibly many dimensions
μ 1/million
α the first variable that comes to mind; or, there's at least one thing and this is first
β a variable juxtaposed against α; or, there are two things and this is second
Ø null
ω torque or else force field
ς pointlessly confusing
ɖ backtracking or contraint logic programming

ʚ it's your bug or someone else's bug
φ it's my bug
ͺ matching an ascii character permitted as an operator in F#
̗ marks a small mistake

Ξ a table
目 κ a table column
Ɨ a table row

Οορό mapping, iteration, or a circular process
ɸΦ denotes a filter or predicate (ɸ from circumscription)
ɕ iteration predicate; e.g. bool MoveNext
ɒ leaf node in iteration of tree or graph

Ӝ a security descriptor or encryption key
τ XτY: insert X into Y possibly (Y may need to be copied in the process)
어 function to reduce or break up
ɪ declares an integer that automatically grows into a bignum when it exceeds +-2^63
Ω resistance (e.g. ohms or drag in a video game)
γ a complex choice
η I know this is inefficient; I want to get it through unit tests before I optimize; optimize if needed
ʘ xʘ means "the function which tests x"
ι general dynamic type
λ a pure function; a function free of side effects allowing batracking or continuation-safe
Ϟ a spring or wavicle in particle effects
ζ Depreciative; e.g. the following is complex only because of poor design
ɤ Whatever; as in, I shouldn't have to do this but I'm doing it because it appears necessary to reach a goal

A model of human subjectivity (just for fun)
Ψψ A model of subjective reasoning or human emotion which is descriptive rather than normative
γ Choice
ω Spin; a self-serving description; the charismatic leader who creates a "reality distortion field"
χ chi-square independence test
δ external blame (angry at her for screwing things up)
ʘ resonant; "yes"; perpetuates increasing commitment
Ϟ dissonant; "no"; rejection; learning may involve structural change
Ϫ a nice surprise given or received
ƴ emphatic "yes" or "thanks alot"
Ƴ "yes" or thanks
ʁ A sense of satisfaction or meaning which involved effort; the unfolding beauty of a pursuit coming from flow
ɣ disproportinate effort; either far too much or far too little
Ʀ Money is king (for calc'ing business plans)
α dominate
β there are two things and this is second
ɐ an exception
λ wavelength of light; a super-intelligent shade of blue (HGTTG)
Ӝ the restaurant at the end of the universe (also HGTTG)

If I have to do something annoying to get myself to write a test suite or something I sometimes play with characters a bit.

Disclaimers: obviously there are punishments and a special ring in hell (see Dante's inferno) for those who abuse Unicodes. If you're in a special domain that assigns meaning to symbols or Greek letters, it's important to stay consistent with that specialty's semiotics or they won't understand what you're doing.

What I tell fellow students (so I'll remember): abusing Unicode can get one fired or thrown off a project. Abuse is when others have to maintain or use your software and the Unicode obfuscates. No one wants to see lots of F# littered with Ӝ (pointless complexity).

I wouldn't share this with RPG graduates in C# land or VB land, but here we already have enough rope to hang ourselves, so this is just potentially clarifying and fun. (Fun is the only antidote I've found to Linux-loving fellow students distrusting M$FT and calling it M$FT in e-mails and so forth. Concise but beautiful graphics is even better (anyone up to a flam3 implementation in F#? my particle effects end up looking like insects ☹)).

But how do you search and replace λ in your code? Create a VB Macro under VS tools and select explore. Insert something like this:

Option Strict Off
Option Explicit Off
Imports System
Imports EnvDTE
Imports EnvDTE80
Imports EnvDTE90
Imports System.Diagnostics
Imports System.Windows.Forms

Public Module qyLibraryMacros
Sub InsertL()
Dim selection As EnvDTE.TextSelection
Dim editPoint As EnvDTE.EditPoint
selection = DTE.ActiveDocument.Selection()
editPoint = selection.ActivePoint.CreateEditPoint()
SendKeys.SendWait("{λ}")
End Sub
End Module

If that doesn't work try:

Dim selection As EnvDTE.TextSelection
Dim editPoint As EnvDTE.EditPoint
selection = DTE.ActiveDocument.Selection()
editPoint = selection.ActivePoint.CreateEditPoint()
editPoint.Insert("{λ}")

Then use tools->customize->keyboard and assign your keys of choice (I use control-number or ^Q to prefix my alternate alphabet; ^Qc inserts a copyright message and I use ^Q^anyletter to insert F# snippets.

I tried to stay away from accents over vowels because those are needed in the domain of localized discourse.

I'll track Unicode adoption on a web site if anyone wants to start establishing domain-specific conventions.

I almost forgot: Hebrew and other languages happen to not quite work in VS. At first it seems like they mess up the left and right arrow keys but after a while you'll see the pattern. Sprinkling someone's code with these characters isn't funny-- unless of course they won't let you program in F# of course.

Also a few of the characters above cause Visual Studio to change character spacing for an entire line. Spacing is very important to know where identifiers start and end.