UFO huh? Any more details available? :-)

What's the general opinion/best practice on this?

Didn't keep it since none of the other grassy traffic islands have curbs marked

I found directional arrows on sidewalks pretty confusing without digging into the tags, likely even worse for end users who don't know the internals of OSM ("directional footways??").

Not sure what the next best thing would be without extra geometry.. There is a cycleway:oneway=* tag described in docs.