A saltire is a diagonal cross, like the letter X.
Saltires are often used in flags and coats of arms.
Examples:
The flag has a red saltire on a white background.
The coat of arms has two blue saltires.
She drew a yellow saltire on the paper.
The knight's shield has a silver saltire.
The flag with a black saltire is very old.
The yellow saltire is very big and looks like a star.