I’ve seen different descriptions of this wooden struction at the junction of Mamalahoa Highway and Waikoloa Road. Most descriptions say it’s either a sundial or a stylized sail.
In reality I remember the structure’s purpose as being much less sexy. It’s a sign post. When I first moved to the Big Island in 1990 I remember driving past this and on the flat surfaces it had the Waikoloa logo on each side. It was a marker sign so you knew where to turn down Waikoloa Road if you were driving north or south on the highway since this was before anyone had GPS navigation built into their car or brick cellphones and your best source of navigation was probably a fold-out map bought from a gas station or a visitor’s guide picked-up at the airport. I’m pretty sure the logos, which were cutout around the flower shape, were taken down a few years after I got to the Big Island.
The set-up doesn’t really lend itself to being a sundial as it’s on a hill without a good level area around it to view the shadow cast for the hours. It doesn’t really look like much of a sail, maybe a jib if anything and certainly not the graceful curves of a Polynesian type of sail. It’s more like a lele (altar) or sign post you’d see in Bladerunner.
I haven’t been able to find any images of this sign post with the logos online, there are probably some tucked into an old brochure of the Waikoloa Land Company someplace or of Waikoloa Village Association, etc.