What will happen if I have a swastika in one of my books when I visit a country where it is illegal?

You could offer this explanation from the book Mankind's Search for God by Jehovah's witnesses. (See jw.org)

Jainism—Self-Denial and Nonviolence is a religion that uses the ancient Indian swastika symbol, was founded in the sixth century B.C.E. by the wealthy Indian prince Nataputta Vardhamāna, better known as Vardhamana Mahāvīra (a title meaning “Great Man” or “Great Hero”). He turned to a life of self-denial and asceticism. He set out naked in search of knowledge “through the villages and plains of central India in quest of release from the cycle of birth, death, and rebirth.” (Man’s Religions, by John B. Noss) He believed that the salvation of the soul could be achieved only through extreme self-denial and self-discipline and a rigid application of ahimsa, nonviolence to all creatures. He took ahimsa to the extreme of carrying a soft broom with which he could gently sweep away any insects that might be in his path. His respect for life was also to protect the purity and integrity of his own soul.

His followers today, in an effort to improve their Karma, lead a similar life of self-denial and respect for all other creatures. Again we see the powerful effect on human lives of the belief in the immortality of the human soul. Today there are fewer than four million believers of this faith, and most are in the Bombay and Gujarat areas of India.

Are you sure you know the difference between the religious symbol and the swastika?

The swastika is a rotated copy of the religious symbol.

is @ a letter "a"? Yet they look quite similar.

If the country you visit have a law something like that just make sure you don't bring it in your journey if you want to get pass easily. Yeah just simple like that. What most important things is your heart. :)

They will probably arrest you, but you may be able to talk your way out of it if you cover it up, which you should do to begin with.