I'm enjoying this thread immensely. Ptradeco says it well:
The key is to match the right shield, aesthetically always, historically not necessarily, to the pattern and size of that pattern.
I do tend to prefer "simple," but that can be very subjective. If a shield and knife pattern/covers work well together, nothing draws attention to itself in the wrong way. I can't always pinpoint why a design pleases me, but am bothered if/when something is visually distracting.
... I generally prefer shields with very clean lines. The one that Ken put on the Junior Michigan Pen he made for me is one of my favorites, and not a shield I've seen often.
Ken has a remarkable eye for proportion, whether of shield, the actual jigging on bone, the curves, etc. :thumbup:
Here are some other shields-- on these
specific knives, where applicable-- that caught my eye as I browsed this thread:
I especially like this particular one because it goes so well with the etch...
Of my modest collection its definitely this one, my newest and maybe nicest knife...
All hail the GEC acorn.

I, too, love the juxtaposition of the acorn shield with the hungry squirrels ('cause you know they are!) on the blade etch. The effect is especially perfect on these little 25s. Not that I'm biased, or anything.
... I'll look for a copy of the book. Does it give a name for this one?? The one on the left. I've wondered about it... is it a plus size "bodice"? Or something completely different?
I was going to add that the shield on the left is colloquially known as the Hefty Helen ("Wholesome Helen" if the inspiration happens to be nearby), but having entirely made that up, I decided to desist.
Of my own modest collection, I would prefer the older(?), more "utilitarian" upper case CASE logo shield that is still on some current production models to the swirly one that is on my Case knives.
The diamond on my trappers is too small, or appears so with the letters smooshed into it:
I like the centered UN-X-LD logo shield on my White Owl, and believe it would look nekkid without it:
The no-shield look is sometimes fitting, as when a small barlow has this much bolster:
I love the blank Tidioute bar on the Appaloosa Jack-- all the more after seeing what it looks like with TIDIOUTE stamped through its middle.
The guitar shield is a funny one, on a funny knife. I wouldn't have bought the above Tango had it not had the guitar shield, but I can't say the shield itself is a favorite. I'd like it more if the guitar head were more pronounced. Maybe.
Fortunately, in the midst of so many other patterns and renditions of traditional knives that evoke appreciation (and respect) for design and craftsmanship, "It makes me laugh" remains a valid reason to like something. Although this one is closer to, "I make me laugh because I bought this one instead of one in subdued, exquisite bone, and I don't regret doing so."
Silly shield.
~ P.