א (Aleph, the first letter of the Hebrew alphabet) stands for the famous Codex Sinaiticus (sometimes designated by the letter S), one of the two oldest copies (apart from the papyri) of the Greek Bible.
This page shows folio 6r of quire 45, Isaiah 52.5-54.1. (Note the Greek passage number references in the left margin of each column. Starting with verse 1 (Α̃ in the margin of column 1 verse 1.) of Isa.1.1 HERE.)
Text in uncial MSS were written without word spacing.
The passage of Isaiah on this folio is that of the Suffering Servant. (Isa.52.13-53.12.) It begins in column 2, first greek numeral ΤΝΔ (354) in the left margin (Isa.52.13.):
ΙΔΟΥ ΣΥΝΗΣΕΙ Ο ΠΑΙΣ | ΜΟΥ ΚΑΙ ΥΨΩΘΗΣΕ|ΤΑΙ ΚΑΙ ΔΟΧΑΣΘΗΣΕ|ΤΑΙ ΣΦΟΔΡΑ
Behold, my servant shall understand, and be exalted, and be exceeedingly glorified.
(It is the LORD speaking.) The next passage (Isa.53.1), number ΤΝΕ (355) begins:
ΚΕ ΤΙΣ ΕΠΙΣΤΕΥΣΕΝ | ΤΗ ΑΚΟΗ ΗΜΩΝ
O LORD, who has believed our report?
(It is the people speaking.)
The next passage (Isa.53.4) begins in column 3, marginal number ΤΝς (356):
ΟΥΤΟΣ ΤΑΣ | ΑΜΑΡΤΙΑΣ ΗΜΩΝ | ΦΕΡΕΙ ΚΑΙ ΠΕΡΙ ΗΜΩΝ | ΟΔΥΩΑΤΑΙ
He bears our sins and our pain ...
The next section (Isa.53.7) marginal number ΤΝζ (357) begins:
ΩΣ ΠΡΟΒΑΤΟΝ Ε|ΠΙ ΣΦΑΓΗΝ ΗΧΘΗ
He was led as a sheep to the slaughter ...
The whole series of passages can be viewed in context HERE, and compared with the Hebrew text HERE.
More about Codex Sinaiticus HERE, especially (from the Sinaiticus web-site!) HERE. And read also (for Greek numerals) HERE.