The easiest way to create a checkmark with Windows is by actually creating the square root symbol. This is quite easy to do, and looks just like a regular check mark (√). See?
To do this in Windows, simply hold down "Alt" and press the numbers 2-5-1 and the check mark will appear. This is handy for any number of things that you may be doing. If you have a task list open in a Word document and want to check off what you do as you go, simply put in that symbol and you'll know that you're done with that task.
The Mac computers work similarly, where the easiest way to produce a check mark is by using the square root symbol. Just hold "option" and press "v" and it should appear.
For both of these, that's the simple way to use a keyboard shortcut to produce something like looks like a checkmark. There is a way to produce an ACTUAL checkmark, but to my knowledge, there isn't a keyboard shortcut assigned for it.