user: Question: Which sign had a Yellow background and a Triangular shape?
Columns: ['Type of sign', 'Shape', 'Border', 'Background colour', 'Text/Symbol']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Warning', 'Triangular', 'Red', 'Yellow', 'Black']
SQL:

assistant: SELECT "Border" FROM "Table" WHERE "Background colour" = 'Yellow' AND "Shape" = 'Triangular';