Four accidentals or more

Signatures go on adding accidentals in the same order you already know, and the trick for naming them does not change: with sharps, the tonic is a semitone above the last one; with flats, the tonic is the second-to-last flat in the signature.

• Four sharps (F♯, C♯, G♯, D♯): E major.
• Five sharps: B major.
• Six sharps: F♯ major.
• Four flats (B, E, A, D): A flat major.
• Five flats: D flat major.
• Six flats: G flat major.

From four accidentals on, counting from the start every time stops paying: recognise the shape. Four sharps end on the D5 line; four flats zigzag down to the D4 space. Here they come in both clefs.

There are signatures of seven accidentals (C♯ major and C flat major), but they are rare and sound the same as simpler neighbours; six is more than enough to read almost anything.