Open the International preferences. Click on the Input Menu tab. Check the boxes for Character Palette and Keyboard Viewer. A menubar item will appear from which you can select each. The Keyboard Viewer is easy to use at it will show you what keys will produce when pressed for any font. Select Wingdings from the drop down menu. You will see numerous characters of which the symbols you want are displayed. If you then use the WingDing font you can insert those characters in the text. If you use the Character Palette you can even select a character and directly insert it: ⌘, ⎇. These are available under Symbols/Technical Symbols.
Below are the Unicode hex numbers for the most common symbols used to represent Mac control keys. You can type these by finding the numbers in the Character Palette or similar font inspector program, or by using the Unicode Hex Keyboard (key in Option plus the number). Lucida Grande is a good font to use.
you need to switch your input to Unicode Hex. that's done in system preferences->international->input menu (I think Kappy mentioned that). go there and check the check box next to Unicode Hex Input. I would also check the box "show input menu in the menu bar" at the bottom for easy switching. Now switch to unicode in the menu bar, hold down option and enter 2318. what you'll get is ⌘
(I just did that).