Frost Crack
Not specified.  Rule of thumb: If tree will degrade slowly (and maintain quality over time... Minor or Moderate). UGS if severe.

Frost Crack: UGS
Spine Tooth (Northern Tooth) Fungus: UGS.

Spine Tooth Fungus (Northern Tooth)
UGS
Why?  The fungus attacks the heartwood compromising structural integrity. Common species associated with this fungus by preference are
Sugar and Silver Maples, Beech, Birch and Oak.

Frost Crack (and Seams):
Moderate Defect
Will degrade slowly.
UGS (unacceptable growing stock) if severe.

Beech Scale Disease:
Indicators of UGS include... crown dieback, cracks, deformation, yellowing of leaves in canopy in addition to root/stem injury.
High-Risk Selection to reduce spread and salvage timber.

Root Wounds/Damage:
Indicators of UGS include... crown dieback, fungi, cankers, cracks in addition to root/stem injury.

Spiral Seam
Moderate Defect (Ontario Tree Marking Guide)
AGS if the tree will degrade slowly.
UGS if severe because it will affect structural integrity. A seam or crack that penetrates >2 inches into the bole creates further fragility by allowing moisture and fungi to enter leading to internal hollowing.
However a seam that has been overgrown with callus material (no active rot) may not cause immediate failure. 
Add Beech Bark Disease into the mix (as the example provided has, the tree is heavily infested and will likely die within a decade and is flagged as UGS to be removed).

Hoof Fungus
Also known as False Tinder Fungus
Major Defect: Always UGS according to OMNRF
(unless retained as a wildlife tree).
Variability: It takes decades to cause significant structural damage however one conk indicates an established fruiting colony. The fungus produces a white rot causing a slow decline by making the wood brittle, soft and susceptible to breakage.
It becomes UGS when it has lost significant merchantable volume or cannot maintain quality before the next cutting cycle, or is simply hazardous due to risk of falling.
Found on Birch and Beech (very common) as well as Maple and Poplar.

Mechanical Damage (Stem Wounds)
Abiotic defect.
UGS if severe.
Considered major or serious because in the example provided it covers a surface area greater than the square of the DBH. 
Greater than 1000cm³ (32 x 32 cm) considered serious regardless of the trees size. Chance of decay increases with ground contact.
Sometimes used and known as bumper trees on active logging roads, targeted for removal in an improvement cut.

Late Fall Polymore/Resinous Polypore
Significant defect (introduces brown cubical rot) severely weakening the structural integrity.
Generally grows on dead or dying trees and stumps but poses a threat to living trees by causing internal rot weakening foundational tissue, leading to thinner crowns or sudden failure without much external warning.
Oak trees usual candidate.

Shoestring Root Rot
Also known as Honey Fungus (a branch of Armillaria)
If you see them at this stage in the example on a standing tree then they have matured to significant root or butt rot. Rhizomorphs (shoestring) radiate out from the established fungal colony (often at the tree base) and spread via contact with another tree, root system or wounds. Removal to prevent spread in forest projects ideal. Extremely destructive fungal disease because it attacks the roots causing decline and death.
Rhizomorphs are named for the black shoestring-like fungal structures which are structures made of tightly bound hyphae (fungal filaments) that act as a nutrient and water transport system. Visible to the naked eye they resemble shoe laces or cords to facilitate growth in new areas, dry conditions, breach obstacles and thus impact forest ecosystems causing root rot.
Hosts include: Fir, spruce, birch, maple, oak and poplar.

Lightning Injury
AGS
Moderate defect
Splitting of the crown/tip.
The next slide has the best sample I have ever found for UGS by stark contrast.

Lightning Injury (hollowed)
Technically considered a Moderate defect under the Ontario Tree Marking Guide classification system however the lightning strike hollowed the inside leaving the structure vulnerable.

Whiteface Scar
Minor Defect usually AGS
This stem has questionable structural integrity and would classify as UGS.
Trunk with scar patterning (layer beneath the bark) of white or light face-like shape (pareidolia) due to exposed wood

White Pine Weeble

Foam

After a heavy rain period foam may accumulate at the base of pine trees (as shown) often referred to as stem flow.

Dry periods: Dust accumulates (containing alkaline particles/salts). Plant residues (acids) and sometimes air pollutants settle building up on the rough bark.

Heavy rain: water runs down the tree trunk (stemflow) collecting the residues (salts, acids, organic compounds).

Saponification (foam) becomes when the turbulence of water running over uneven bark mixes with fatty acids in the pine bark/sap (containing alkaline salts).