Hi there, Laura:
If you are not able to replicate a symbol with your keyboard, you could use brackets. For example, type [checkmark] in place of the symbol in the document. Similarly for a line that is crossed out, simply type [crossed out text] next to the words that are crossed out.
Thank you for your contributions!
Community Manager, National Archives Catalog
If you are on the Apple Macintosh platform, checkmarks can be created with the key combination CTRL+V..
Hope this helps.
...oh, and "strikethrough" is the other formatting command. If you select the text you wan't to 'strikethrough, There should be a command to do that in most word processors. In OpenOffice you can find it here: Format menu | Character... | Font Effects tab | Strikethrough drop-down.