For example, the coat of arms of Finland: "Gules, semy of roses argent, a lion rampant crowned Or trampling a sabre in base proper, his dexter foreleg in the form of a man's arm vambraced and embowed argent garnished Or bearing aloft a sword proper."
And somehow from this emerges a special lion with a sword through it's head: https://satwcomic.com/coat-of-arms
Translation:
Gules: Red
Semy: Background
Roses argent: Silver roses
A lion: A lion
Rampant: Standing
Crowned Or: With a literal golden crown on its head ("Or" meaning "gold")
trampling a saber: stepping on a saber
in base proper: the saber should be colored normally
his dexter foreleg: The right "arm"
in the form of a man's arm: the right "arm" should be a man's
vambraced: wearing armor about the forearm
and embowed: bent
argent: silver
garnished Or: decorated with gold ("Or" meaning "gold")
bearing aloft: carrying
a sword proper: a sword colored normally
So, in normal speech, this is a basically a technical specification for:
1. The background should be red with silver roses
2. The foreground should be a standing lion
3. The lion should be wearing a golden crown
4. The lion should be standing on a sword, colored normally
5. The lion's right forearm should be a human's, armored
6. The armor of the forearm should be silver with gold decoration
7. The human-like right forearm should be bent and raised, carrying a sword
8. The sword should be normally colored
Anyone who knew heraldry when it was important would be able to take that description and churn out a reasonable facsimile of the crest.
The lion isn't stabbing itself in the head any more than a "suicide king" is.
And I got confused when GRRM started using proper heraldic descriptions for flags in ASoIaF with the third book, while the two before were basically just very simple English descriptions. Most readers probably never really noticed :)