According to the 1935 trail maintenance book, the upsidedown ! is the standard FS blaze. They even have dimensions for it. Maybe you are seeing the result of poor axemanship? Blowdown damage? Or even pre or post-FS blazing. They are also supposed to be on both sides of the tree, but I've seen trees blazed on the trail facing side only...
I noticed on the the trail to Anvil Lake 3 notched blazes at the lake TH. Wonder what the heck that means? Water I guess, maybe pre Forest Service.
Blazing seems like a great idea, I wonder why the practice was dropped. Certainly does no harm to the tree.
Hey, check it out, from Trailadvocates no less - 3 blazes on the old Skyline Trail:
http://sinope.redjupiter.com/images/trailadvocate/DSCF0880.jpg