Martial Shield Familiarity is a Shield Familiarity. This allows the use of all Shields, those covered under __ and all heavy shields; Heavy Shields all have extra Resilience and can mount weapons and other materials (probably requiring a separate proficiency to use). Using specific areas efficiently and creatively is covered under the Martial Shield Familiarity.
This familiarity also allows a character to use ANY shield as a weapon, with full Attribute and proficiency bonuses for attack and damage. The full Bash Factor of Shields can be added assuming it can be employed without penalty.