I want to know where it comes from, what it is actually supposed to be (or stand for) and if at all possible what is it known as?

i've been searching on this for ages but cant find anywhere with any sort of description on this symbol. there are many learned metal folk here who i am sure must have the answers i'm looking for.

no but I found this by typing in speed metal logo into google

http://www.nolifetilmetal.com/heretic.htm

As far as I know it originated when a Canadian record shop in Montreal called "Rock en Stock" which imported metal LP's, also licensed and bootlegged LP's as "domestic" versions (thus adding the Banzai label/logo). They often came with no lyric sheets, and they all got pressed at limited copies (around 500 each). They also released some tapes There were 18 LP using it in total I think:

Iron Angel - Hellish Crossfire
Destruction - Infernal Overkill
Destruction - Sentence Of Death
Hellhammer - Apocalyptic Raids
Celtic Frost - Morbid Tales
Bathory - Bathory
Kreator - Endless Pain
Bathory - The Return...
Living Death - Metal Revolution
Kreator - Pleasure To Kill
Thrust - Fist Held High
voivod - war and pain
Warrant - The Enforcer
Running Wild - Branded & Exiled
Tyrant - Mean Machine
Possessed - Seven Churches
Voivod - Rrroooaaarrr!

Of course, since then many more bands have adopted it! Damn cool sigil!