A family of Microsoft word processing software products for creating web, email, and print documents.
This is what works for me:
- Insert > Symbol > Advanced Symbol
- Select font "Wingdings"
- Click on any of the squares on the third row, or the one on the fourth row (the last one is the one I use)
As mentioned by Bob, there is a narrower version of the square (a rectangle, actually) that is non printing as its ASCII code is that of the DEL (delete) key. In the Symbol character palette, it's located between the **~**and the Ä and it should not even be listed. Some fonts show it as a blank space.