The sign said "Keep off the grass".
Questions (1) Comma after "said"? The sign obviously didn't speak, so omit comma? (2) There was no terminal punctuation (full stop) after "grass", so full stop goes outside ending quotes? (3) If the sign did have terminal punctuation, period goes inside like this, right? The sign said "Keep off the grass."
And, would a comma follow "read"?
The sign read, "Keep off the grass".