I've copied an icon to my customized toolbar.
Tools|Customize|Commands tab
Format category|Lock Cell (it looks like a padlock)
I dragged this to a toolbar. Now when I click on a cell, that icon is either
engaged or not engaged--depending on the "lockedness" of that cell. (I find
this the easiest and quickest.)
If you're not using Format|conditional Formatting for anything else, you could
use that too:
Select your range and do Format|Conditional Formatting.
Then Formula is: =CELL("protect",A1)
Set a nice pattern and click ok.