Shimano large chainring "for bashguard"; what's the difference

Some Shimano large chainrings are spec'ed as "for bash guard", and some don't mention bash guard at all.
What's the difference with this type of chainring?




1. I have seen a Shimano chainring with a bash guard; on the centerline facing, there seem to be four phillips head screws.
2. For "regular" chainrings, can you add a bash guard after-the-fact? (Are the four phillips head bolt holes missing?)