Is there a unicode character for the Windows key?

For non-techies on Facebook, use workaround seen on Wikipedia: ⊞ Win.

Since you want to display the character on the Facebook where you have no control over fonts and there is no such character in Unicode at the moment, you can use mathematical operator Squared Plus (code point 229E) to imitate Windows logo as Wikipedia does in article on Windows key and in other keyboard-related articles.

Excerpt from the article:

• ⊞ Win opens the Start Menu

• ⊞ Win+D shows the desktop (hiding even non-minimizable windows), or restores hidden windows when pressed a second time.

• ⊞ Win+Tab ↹ cycles through taskbar buttons. This key combination is reassigned in Windows Vista.

I am doing it that way.

You have two options: you can use the character available in the Marlett icon font, which is the font that Windows itself uses to draw its icons, and is therefore the most authentic way to render the symbol, or you can use Win to symbolise the key.

Win is the most commonly-used due to its convenience, especially inside of the industry, but since you say your audience is likely to be technologically illiterate, it would be more safe to go for the former and render the actual symbol like Windows does.

Using the Marlett Windows symbol in Microsoft Word

If you're using MS Word, you can insert the icon directly into your document.

1. Click the Insert tab.

2. Click the Symbol button.

3. Select the Marlett font by typing it in or selecting it in the dropdown.

4. In the Character code field, type 87, then press Insert.

Using the Marlett Windows symbol in other applications

If you're using something other than Word, you can use Windows' native Character Map to copy the icon to the clipboard and then directly into the program you're using.

Search for the Character Map in the Start menu's search bar. Once it's open, select the Marlett font from the dropdown. In case you don't notice the Windows key instantly, search for a character code of 0x57.

I like ❖ (U+2756 - BLACK DIAMOND MINUS WHITE X)

In windows 10 there is a new on-screen keyboard.

1. Display the keyboard : ⊞ Win .
2. Select the symbol tab Ω
3. Select the math symbol page ∞
4. In the middle of that page you'll find a window ⊞

I works with pretty much any application, here in the google search bar: